The United and England international centre-back was not named in the squad for the match at Old Trafford on Wednesday night triggering rumours that he had suffered a recurrence on a groin injury.
However, Fergie has explained that he had merely decided to rest Ferdinand and that he is not injured.
"The fact Rio had played extra time in the FA Cup semi-final against Everton after only just coming back from two or three weeks out meant it was too big a risk," Fergie said.
"There was nothing wrong with his groin, it was just tiredness."