3. Tracy McGrady
The Rockets' acquisition of Tracy McGrady during the 2004 offseason was intended to give Yao Ming a superstar pairing. T-Mac had led the league in scoring in consecutive seasons prior to his arrival to the Space City and was viewed in the same stratosphere as Kobe Bryant at the time.
Although the Rockets had several great moments with T-Mac, the Yao-McGrady pairing never quite lived up to its potential. This is because injuries to both stars limited their time on the court, as McGrady missed nearly half of the Rockets' games in 2005-06 and 2008-09.
As for Yao, he missed 86 games between 2005-2008, which was when McGrady was mainly healthy. The Rockets' best bet would have been to have moved McGrady after the 2006-07 season, as he was coming off three consecutive seasons of averaging at least 24 points in Houston, and had even posted a career-best 6.5 assists per game, which ranked 12th in the league.
By that point, the Rockets had seen three seasons of the McGrady experience and the results were quite underwhelming, as the Rockets were first-round outs in two of the seasons and even missed the playoffs during the other.
McGrady still had peak value, and the Rockets could've tried their hand at pairing Yao with another superstar. Instead, the Rockets waited until 2009-10 to move him, which was far too late, as he didn't have any value after missing 47 games and averaging just 15.6 points during the previous year.