Les, who departed last week's Premiership game against Everton with concussion, locked his neck during the week and missed out on our 5-1 triumph against Chelsea.
Our top-scorer with 14 goals so far this season said the problem had started to settle down but Glenn, speaking at Thursday's press conference, was cautious.
"That will be a late decision," he said. "Les has a locked neck, it's been released a little but it's still in spasms.
"We're hoping it will settle down properly but that was why he missed the game agaiunst Chelsea, not through scans or neuro surgeons saying he couldn't play, but from that neck problem."
Dean Richards, cup-tied in midweek, would have probably returned anyway but Glenn revealed that Anthony Gardner suffered an ankle knock against Chelsea that made him a 'slight doubt' for Saturday.
That leaves Christian Ziege, Steffen Freund, Stephen Carr (all knee), Stephen Clemence (groin), Goran Bunjevcevic (thigh), Gary Doherty (broken leg) and Chris Armstrong (hernia) on the missing list.
For Bolton, Dean Holdsworth and Paul Warhurst are both available after serving three-match bans.
However Holdsworth (thigh) and Warhurst (calf) both sustained injuries in a midweek reserve game and their fitness will be monitored overnight.
Simon Charlton is also doubtful with a calf strain while Colin Hendry and Per Frandsen have already been ruled out.
Glenn Hoddle will leave it late to make a decision on Les Ferdinand for Saturday's FA Cup tie against Bolton.