Rooney began Saturday's 1-1 draw with Liverpool on the bench, with Ferguson claiming that the striker was "devastated" by the three-match suspension he was handed for next year's European Championships.
Meanwhile, captain Vidic has not featured for the Red Devils since the opening day victory over West Bromwich Albion.
The centre-back picked a calf injury at the Hawthorns but has now made a full recovery.
"I think Wayne's ready," the boss told a press conference in Bucharest. "When he came on [against Liverpool] I thought he was bubbly, full of energy and enthusiasm. He was desperate to get on, which was good.
"Rio [Ferdinand] played very well on Saturday but we have Vidic with us here and I felt it was a good opportunity to give Rio a break. Playing three games in seven days is a lot to ask."
United have drawn their opening two matches in the competition.