Here's a look at the transactions this week that had the most significant fantasy impact.
Alex Gonzalez, SS – placed on the 15-day DL (right knee)
Edwin Maysonet, IF – contract purchased from Triple-A Nashville
Impact: The Brewers' everyday shortstop could miss the rest of the season after he suffered a torn ACL during Saturday's game. He has shown a decent power the last couple years, slugging a combined 38 homers over 2010 and 2011. Unfortunately, he rarely hits for a solid average, as his .247 career batting average attests. This year, he has hit four home runs with a .259 batting average. Orioles castoff Cesar Izturis should get the bulk of playing time at shortstop for the Brewers, at least until they find a better option. He is only worth consideration in the deepest of NL-only fantasy leagues due to his weak bat. Maysonet is a 30-year-old career minor leaguer who will act as bench depth.
Juan Rivera, OF – placed on the 15-day DL (hamstring)
Scott Van Slyke, OF – recalled from Triple-A Albuquerque
Impact: Rivera will miss at least a couple of weeks after suffering a serious hamstring strain Tuesday. His numbers the last couple years have been mediocre, as he posted a combined batting average of just .255 with 26 home runs in 256 games between 2010 and 2011. He was faring no better this year, hitting just .247 with two home runs in 25 games before the injury. Newly acquired Bobby Abreu should get the majority of playing time in left field in the meantime. Abreu has seen his batting average take a nosedive in recent years, hitting below .260 in back-to-back seasons entering 2012. He also set a career low in home runs last season with just eight long balls in 142 games. However, he hasn't stolen fewer than 20 bases in a season since 1998, so his speed alone could make him worth a look in deeper leagues. Van Slyke should see limited playing time, but has the potential to post some decent numbers if given the opportunity to play regularly.
Aubrey Huff, 1B-OF – activated from the 15-day DL
Guillermo Mota, RHP – placed on the restricted list
Impact: Huff returned to game action Monday after missing a couple weeks with an anxiety disorder. After a disappointing 2011 season, he started this year slowly, hitting just .182 with a home run and four RBI in 12 games. He should see time at first base and left field, cutting into the playing time of Brandon Belt, Brett Pill, Nate Schierholtz and Gregor Blanco. Mota has been suspended for 100 games after a second positive test for a controlled substance. His agent claims that the positive test was a result of Mota taking children's cough syrup, but he'll miss most of the season regardless. He is 0-1 with a 5.06 ERA in nine relief appearances.
Jayson Werth, OF – placed on the 15-day DL (wrist)
Ryan Zimmerman, 3B – activated from the 15-day DL
Impact: Werth will be out of action for at least three months after he broke his left wrist while attempting a catch during Sunday's game. He had a disappointing debut season for the Nats in 2011, as he managed a paltry batting average of just .232. He did slug 20 home runs and steal 19 bases, so his season was still valuable to fantasy owners. In 27 games this year, he hit .276 with three homers and three steals. Roger Bernadina and Xavier Nady should receive extra at-bats due to Werth's injury, though neither player is likely to offer much in terms of fantasy value. Zimmerman was off to a rough start this year before missing a couple of weeks with inflammation in his right shoulder. In 15 games, he was hitting just .224 with a home run and seven RBI. Stephen Lombardozzi filled in nicely at third base while Zimmerman was on the shelf, and was hitting .305 with no home runs and four RBI through Sunday's game. He should continue to receive a decent number of at-bats while being used at various positions.
Huston Street, RHP – placed on the 15-day DL (right lat)
Miles Mikolas, RHP – contract purchased from Triple-A Tucson
Impact: Street has been dominant as the Padres closer this year, converting all four of his save opportunities while posting a 0.93 ERA and striking out 13 batters in 9.2 innings. A strained latissimus dorsi muscle will keep him out of action for now, and though he won't require surgery, he also doesn't figure to be ready to return after the 15-day minimum. Dale Thayer inherits the closing job in San Diego, but he's a 31-year-old career minor leaguer with just 23 major league appearances under his belt coming into this season. He's still worth a look as long as he's picking up saves, but fantasy owners should be ready to cut him loose if he loses the closing gig.
Jonathan Sanchez, LHP – placed on the 15-day DL (left biceps)
Johnny Giavotella, 2B – recalled from Triple-A Omaha
Impact: Sanchez has had serious issues with his control so far this season, walking 22 batters in 25.1 innings. Those control issues led to a poor 6.75 ERA and an awful 1.86 WHIP. He has been diagnosed with tendinitis in his left biceps, so he'll be out for an as yet undetermined time. Luis Mendoza appears to be the most likely candidate to fill the vacant spot in the rotation, though he's not likely to help a fantasy team due to his ugly career numbers. Giavotella figures to share the second-base duties with Chris Getz. He was expected to be the regular second baseman for the Royals this year, but failed to make the team out of spring training. He has shown an ability to hit for average in the minors, but with little power and unremarkable stolen base numbers.
Doug Fister, RHP – activated from the 15-day DL
Brayan Villarreal, RHP – optioned to Triple-A Toledo
Impact: Fister ended up missing a month after he strained his left side during his first start of the season April 7. He was lights-out last season after his trade to the Tigers, going 8-1 with a 1.79 ERA in 70.1 innings. He looked sharp Monday in his first start off the DL, pitching seven shutout innings against Seattle. His mediocre strikeout rates are cause for concern in leagues with innings limits, but his potential for a solid ERA and WHIP still make him worth owning in mixed leagues. Villarreal appeared in four games with Detroit, giving up a hit, two walks and no earned runs in 1.2 innings.
Justin Morneau, 1B – placed on the 15-day DL (left wrist)
Brian Dozier, IF – contract purchased from Triple-A Rochester
Impact: Morneau has not been the same since he suffered a concussion during the 2010 season. Going into that season, Morneau had driven in at least 100 runs four consecutive seasons and had a .280 career batting average. He started strong in 2010, hitting .345 with 18 home runs and 56 RBI in 81 games before a concussion ended his season prior to the All-Star break. Since then, he has experienced ongoing symptoms and has hit just .228 with eight home runs and 39 RBI in 89 games between 2011 and 2012. He's been acting as the Twins' primary designated hitter and will miss some time due to a sore left wrist. He could return as early as May 16. Dozier should see a fair amount of time at shortstop, but is not likely to have much fantasy value due to his lack of power or stolen base potential.
Danny Valencia, 3B – optioned to Triple-A Rochester
Darin Mastroianni, OF – recalled from Triple-A Rochester
Impact: Valencia couldn't get things going offensively in 27 games this season, as he hit just .190 with a home run and 11 RBI in 100 at-bats. Jamey Carroll and Trevor Plouffe figure to get most of the playing time at third base while Valencia tries to work his way back onto the major league roster. Carroll and Plouffe have combined for a .196 batting average (30 for 153) with one home run and nine RBI through Wednesday, so they aren't likely to do much better. Mastroianni will serve as outfield depth for the Twins.