The 2019-20 season marked Kleber's third season in the NBA and his third with the Mavericks. He appeared in a league-high 74 games, averaging career highs in points (9.1), rebounds (5.2), threes (1.6) and assists (1.2) per game. Kleber also drew 21 starts. The 6-foot-10 big man set career marks in three-point percentage (37.3) and free-throw percentage (84.9). On Dec. 31 against the Thunder, Kleber grabbed a career-high 14 rebounds and added 14 points and two assists. Shortly after, on Jan. 4 against the Hornets, Kleber hit a career-high six three pointers en route to 24 points, four rebounds, two assists and one block. In a win against the Magic on Feb. 21, Kleber scored a career-high 26 points and added three rebounds, one assist and one block. Kleber swatted a season-high five blocks on two separate occasions -- first at Atlanta on Feb. 22 and second against the Pelicans on Mar. 4. During that Mar. 4 victory, Kleber also provided a season-high four assists. On Mar. 2, Kleber registered his second and last double-double of the season with 13 points, 10 boards and two blocks during a close loss at Chicago. During the NBA bubble in Orlando on Aug. 11 against the Trail Blazers, Kleber secured a season-high two steals in addition to 12 points, four rebounds and one block. Kleber started all of Dallas' six playoff games against the Clippers. During the post-season, Kleber averaged 6.7 points, 6.5 rebounds, 1.5 assists and 1.2 blocks in 33.9 minutes per contest.

Kleber had a solid sophomore year for the Mavericks in 2018-19, responding to increased minutes with improved production. The German import played in 71 games and started 18 times. He posted notable upticks in points (6.8), rebounds (4.6) and blocks (1.1) per game. Kleber also showed improvement in his 3-point shooting, hitting at a 35.3 percent clip from long range, which gave him the confidence to take many more attempts (3.1 per game, up from 1.8). He was reliable at the free-throw line, albeit in a limited sample, hitting 78.4 percent of his shots. After mostly playing a rotational role for much of the season, Kleber saw a spike in minutes toward the end of the year and took advantage. He recorded all five of his double-digit-rebounding games in his last 14 games of the year, posting three double-doubles in the process. That included his finest game of the season, when Kleber set a season high with 18 points and a career high with 12 rebounds Mar. 16 against Cleveland. All told, he scored in double digits 21 times.

Kleber came over from the German pro league to sign with the Mavericks ahead of the 2017-18 season. The 26-year-old rookie appeared in 72 games for Dallas, making 36 starts. He averaged 5.4 points, 3.3 rebounds and 0.7 blocks per contest. Despite averaging just 16.8 minutes per game, he scored double-digit points on 12 occasions and blocked multiple shots nine times. The 6-foot-10 stretch four shot an effective 48.9 percent from the floor, including 31.3 percent from 3-point territory. He made 9-of-10 field goals for a career-high 21 points at San Antonio on Dec. 16. Kleber stuffed the stat sheet the day after Christmas versus Toronto, picking up 15 points, eight rebounds, two assists, five blocks and two steals in a 98-93 win. That was his second five-block game within a span of three weeks, as he'd also rejected five shots Dec. 6 against Boston. Kleber posted his first NBA double-double at Philadelphia on Apr. 8, notching 11 points and 10 rebounds.