Rooney (hip) and Vidic (head) missed the Reds' triumphant Champions League semi-final second leg on Tuesday night, while Evra (head) was stretchered off in the game's dying stages.
"Patrice got a real bang on the head," the manager confirmed, "but I'm sure he'll be all right for Saturday.
"Vidic may be okay too, but that's in the doctor's hands."
He also told MUTV: "After getting the knock against Chelsea on Saturday, Wayne was in real pain on Monday.
"I made the decision not to risk him because if I had to then substitute him early in the match it could really have affected us. So I went with a front two of Ronaldo and Tevez.
"Wayne has got a big chance [of being fit for West Ham]. He'll be all right for Saturday."