Ferguson revealed Paul Scholes was on medication for two days before turning out at Eastlands.
For United, it was a reasonable outcome given as late as Wednesday morning, Ferguson still was not sure who was going to play.
"We have done well to get a good team on the pitch," said Ferguson. "The big problems for us were Scholes and Darren Fletcher. Scholes has been on medication for the last two days. He has not trained. Darren only trained [on Wednesday]. It was an ankle injury but fortunately he was okay."
The effects of the virus that has swept through the United camp this week were not obviously evident as they dominated for large periods in a disappointing game.
"I am disappointed we didn't win, we needed to win," Ferguson said. "But we only made two good chances in the game and I don't think they made any. Maybe all the tension in the build-up to the game was too much for it to be a real spectacle. There were good aspects to our play. We dominated and played some good football. But teams coming here are going to find it difficult."