Aston Villa's in-form midfielder Steve Sidwell is a doubt for Saturday's Premier League clash at Blackburn Rovers after suffering a thigh problem, while Ashley Young and Emile Heskey should recover in time to play.
Sidwell sustained the injury during the warm up before Wednesday's Carling Cup clash with Cardiff City at Villa Park.
Villa manager O'Neill said: "I've got a bit of concern with Steve Sidwell. He played splendidly against Portsmouth on Saturday. I was going to keep him back on the subs bench against Cardiff but in the warm up he felt his thigh.
"Even though he was down as a sub on the list, he could not have come on. It was getting sore as he was on the bench so that is be a bit of a concern.''
The former Chelsea player had a difficult first season at Villa but has relished being played on a regular basis alongside Stiliyan Petrov during the current campaign.
O'Neill is hoping striker Heskey and winger Young will have regained fitness for the trip to Ewood Park. They were ruled out of the Cardiff match with ankle and calf problems respectively.
O'Neill said: "Ashley got a kick in the lower part of the calf that was pretty sore. It happened during the Portsmouth game although he was able to continue. But I'm hoping Ashley and Emile will be available. They've done a bit of work.''