The Black Cats skipper has been plagued by a recurring knee injury this term, which has restricted him to just 10 Premier League appearances, and it is likely that he will play no further part in the Wearside clubs relegation battle.
"Lee has a few more days to go after having had the injection," O'Neill told the Sunderland Echo.
"The specialist told him not to do a great deal and while he is obviously working with the physiotherapist, he is not doing anything that will risk damaging his knee.
"We hope for the best but, to me, if he comes back this season, then that would be a bonus - and an unexpected bonus. We may have to cope without him and even if he does successfully come back from the injury, he will still be nowhere near match fit."