Manchester City claimed the ?24million striker has an allergy to certain types of grass and had experienced swelling to his face. He was given two anti-histamine shots at half-time and club medics considered giving him an injection of adrenaline.
Dynamo Kiev 2 Manchester City 0: Read Chris Wheeler's match report
Strange: Mario Balotelli is assessed after complaining of swelling in Kiev
Balotelli appeared to be sick by the side of the pitch and lasted only a few minutes of the second half before being replaced by Carlos Tevez.
Mancini said: 'He had an allergy, I don't know what, his face was swollen.
'He wanted to come out for the second half but he had this problem 10 seconds before coming out for the second half. I came out one minute before the players and I didn't see Mario.
'A guy told me Mario had an allergy after he came out. Mario said: "I can play" but his face was swollen.'
Last night's defeat leaves City's hopes of reaching the quarter-finals hanging by a thread, but Mancini refused to concede defeat in the tie.
He said: 'At Eastlands it will be a different game. Usuallywe don't concede goals like this - we are more professional. We conceded twostupid goals. They played on the counter, so I'm frustrated.'
He added: 'I think we had some problems and I hope that it can improve with the strikers for the return match.
'If the strikers improve and the defenders pay attention maybe we have a chance to go through. Dynamo Kiev were fresher than us. A few of us in the championship we have played (recently) every three days.
'I think that 2-0 is not a good result - we didn't mark well for the first goal, the second goal the same. We were four or five metres from the opponent. When you mark in the box you should be near.'
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