Rio ruled out of League Cup final
The England defender, eligible to play after a four-match suspension, was not in the squad for United's 3-0 Premier League victory over West Ham United at Old Trafford and after the match Ferguson explained that Ferdinand was not fit.
"He (Ferdinand) felt a twinge in his back this morning. We did a warm up at Carrington (training ground) and he felt a twinge and we couldn't risk it. He won't be playing on Sunday," Ferguson told Sky Sports.
A back injury also sidelined the England centre-back from the end of October until the end of January and he has played only three matches since then - one League game, one League Cup match and last week's Champions League game at AC Milan.
Ferdinand was suspended for four league matches after an incident in the game against Hull City and was only eligible to play in the league again against West Ham on Tuesday.