I'm thinking a lot of you might mention D-Rose, but I'm going for Brandon Roy.
There might not be a lot of NBA fans who remembers him, but he was drafted at 2006 by Minnesota Timberwolves but was traded immediately to the Portland Trailblazers, he averaged 16.8 PPG 4.4 RPG 4.0 APG and was awarded Rookie of the Year. He continued to play well for Portland, scored 52 points in a game, made 10 steals in a game, and made 3 All-Star teams. The injury came at the 2010-2011 season, where his knees needed surgery, because it was degenerating, which resulted him missing most of the season. He came back that year and played for the 1st round of the playoffs against Dallas Mavericks, they lost to Dallas. He retired before the 2011-2012 season started, he said that his knees degenerated so much that he decided to retire from basketball.
He made a comeback in 2012-2013, his knees were better and he was signed by Minnesota Timberwolves, problem was he suffered an injury in a preseason game, played 5 regular games before needing a season-ending injury on his right knee. He was waived after and hadn't played an NBA game ever since.
He might be the next Kobe if only his knees had been healthy.
What about you?