Silva on City life
Balotelli was given an antihistamine injection during half-time after his face swelled up, and was eventually taken off shortly before the hour mark in some discomfort.
He was constantly rubbing his face and is believed to be allergic to certain kinds of grass.
"Mario had an allergy, I don't know what, his face was swollen, I don't know why," Mancini said. "He wanted to play in the second half but he had this problem 10 seconds before coming out.
"I came out a minute before the players and I didn't see Mario. He then said he could play but his face was swollen."
Mancini is yet to confirm whether Balotelli will be in contention to face Reading in the FA Cup on Sunday.
Meanwhile, Dynamo Kiev striker Andriy Shevchenko has warned his team-mates to expect a rough ride against in the return leg of their Europa League last-16 tie against City.
Shevchenko, 34, opened the scoring on Thursday, with Oleh Gusev also on target in a 2-0 home win. The result gives Dynamo a useful advantage going into the second leg next Thursday, but Shevchenko is taking nothing for granted.
"This was only the first half. It will be a completely different game in Manchester," he said. "We are very glad to have won. I think our fans really enjoyed this game.
"What was the most difficult thing? Sticking to our tactical plan. We played very well from a tactical point of view, and I must give full credit to our defenders.''