Juan Martin del Potro

ANALYSIS
Del Potro returned from a three-year absence due to injuries earlier this week in Buenos Aires and lost 6-1, 6-3 to Federico Delbonis, and he indicated after the match he was likely retiring from the sport. The 33-year-old's withdrawal from Rio indicates the start of his retirement, though he did say it's possible he could have "another chance to play" at some point if the outlook on his lingering knee injury improves.