Wickham, who made a rare and promising appearance at Norwich City, is on stand-by to make his first start of the season.
O'Neill said: "Fletcher went down to see the specialist but he hasn't done anything yet in training so that's all I can tell you at the moment.
"We're doing a lot of work with Connor and the young players after training but the biggest thing for Connor is that he wants to do it and he wants to improve. He has the physique and natural attributes so it's really up to him.
"Don't start reading everything into a 45 minute performance. I thought he did really well in the Norwich game and he wants to show more aggression.
"Now's the time for him to start performing and getting something out of these games not just letting the minutes on the field pass him by.
"I've been here exactly a year and Connor played in my first game because Bendtner wasn't available.
"He came in and played in the next game and came off injured against Tottenham so he's found his career standing still, certainly at club level, but he's addressing it and that's the most important thing."