Wilfred Bouma is aiming to return to the first team in time to take on Sunderland away on November 19.
Bouma has missed the last three games with a hamstring injury and will not be fit in time for this weekends game against Liverpool. However he could be available for the following game with the break in fixtures due to international games coming in handy for his recovery.
O'Leary said: 'I can't see him being for the Liverpool game - I think we're looking at the Sunderland match at the earliest. It's a disappointment but we have to get on with it. There's nothing we can do. He's injured now and he's going to be out for a few weeks. It's given Jlloyd Samuel a chance and it's down to him - he will be judged on how he takes his chance. If he plays well and does well, he can stay in the team he's got the shirt at the moment. This is the first time Jlloyd has had competition for his place and we'd like to get that more around the pitch.'