Sunderland boss O'Neill admits Johnson wasn't fit for Man Utd clash
The winger convinced his manager he had fully recovered from a knock picked up at home to Reading four days earlier, but failed to last the 90 minutes.
O'Neill revealed: "Adam had a dead leg on Tuesday evening and declared himself fit. I don't think deep down he really was.
"We don't have fantastic options but we'll try to get some of the players fit again if we can.
"If we can't, we'll just have to get on with it."