A bout of concussion against Everton on Saturday has left the in-form striker doubtful for the Worthington Cup semi-final, second leg at the Lane.
A goalscorer in the first leg at Stamford Bridge, Les managed a light run in training today but Glenn said he still felt 'a little fuzzy'.
Glenn explained: "Les has a 50-50 chance. The neuro surgeon hasn't said to us over the weekend that Les can't play, the scans have been looked at and we really have to go by Les's reaction now.
"He has a slight headache, no more than that at the moment. He's feeling a little fuzzy but he's been out for a light jog today and gone back in.
"Wednesday might come around a bit too soon but we don't know. We'll see how he feels tomorrow, see if the headache's gone and see what the surgeon says again come Wednesday morning."
Glenn added that there were no further injury worries from Saturday's draw against Everton. Dean Richards will have to sit out again cup tied.
Glenn Hoddle has revealed this afternoon that Les Ferdinand has a 50-50 chance of lining-up against Chelsea on Wednesday.