Aston Villa are sweating over the fitness of their Player Of The Year Stiliyan Petrov who suffered a dislocated shoulder during the Peace Cup clash with Atlante.
The Bulgarian midfielder, a strong candidate to replace Gareth Barry as skipper for next season, suffered the setback during the first half of Villa's 3-1 success in Spain.
The midlands club expect to find out in the next 48 hours the extent of Petrov's setback and O'Neill told Aston Villa TV: "Stiliyan dislocated his shoulder and our doctor put it back in immediately."
He added: "He is feeling a little better but we don't know just at this moment how much damage he has done. It was obviously the low point of the night.
"But we don't know the extent of the problem. We will find out over the next couple of days to see how it settles down. We just don't know. But it is a concern to us."
Petrov took time to adapt to life in the Barclays Premier League after becoming O'Neill's first major signing in a £6million switch from Celtic during the summer of 2006.
But he sparkled in a holding role last season as Villa clinched a place in Europe for the second successive season.
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