In early November, the 32-year-old Richardson missed four games with a left ankle sprain. On Dec. 26, Richardson did not play in a win over Memphis because of a lower-back injury.
Richardson is averaging 10.5 points and 3.8 rebounds per game.
Damien Wilkins, who has been playing more lately, also missed the game for personal reasons.
Washington began the season with 11 straight losses before getting its first win, and the Wizards went into Wednesday's game with the second-worst record in the league.
However, they have been playing better lately, winning six of their last 10 games before Wednesday night's loss to the 76ers.
This stretch of good play is tied somewhat to the return to health of guard John Wall. The No. 1 overall pick in the 2010 draft, Wall missed the first 33 games of the regular season with a left knee injury.
Entering the game, Wall was averaging 14.6 points, 6.6 assists, and 2.3 rebounds in 10 games.
Collins said that he was happy that the Wizards did not fire head coach Randy Wittman. Collins gave credit to Washington president of basketball operations Ernie Grunfeld for sticking with Wittman rather than firing him.
"I give them a lot of credit," Collins said. "They knew they didn't have their guys. When you are a coach and you are sitting over there getting beat, all of a sudden the whispers about the coach getting fired and all of that stuff start to come up. I'm happy for Randy Wittman."