After seven months out with a broken leg and ankle, big defender 'Doc' returned to a hero's welcome when he came off the bench against West Ham on Saturday.
Doc now has three Premiership games left to prove hit form and fitness to Ireland manager Mick McCarthy in time for this summer's World Cup.
Boss Glenn said: "If injuries happen, which you don't want to see, he could sneak in. He's going to be fitter another six weeks down the line.
"I wouldn't say he's 100 per cent out of the scene if there are injuries and people need to be called up.
"I'd have to be honest with Mick and say he's rusty at the moment, he's not ready for that level of football yet - in six weeks he might be.
"There's no problem with his ankle, that's fine and he's going to continue with reserve football and train hard and see where it takes him."
Glenn admitted Doc had been desperately missed since sustaining the injury against Torquay United in the second round of the Worthington Cup in September.
"When Gary broke his ankle against Torquay it was a massive blow for him and the club, " said Glenn. "Gary is a smashing lad, an honest boy who wants to learn.
"He's really had a tough winter, him and Stephen Carr and quite a few others - too many for my liking.
"He's really worked hard, had four and a half reserve games, but is still a bit rusty and not 100 per cent match fit. Hopefully before the end of the season, and with a good pre-season, he'll be fresh and ready to resume his career."
Glenn joked that Doc and fellow Irish long-term victim Steve Carr - now ruled out of the World Cup - were sick of the sight of each other!
"They've obviously been in that treatment room and in rehab together," he said.
"Certainly they've had to stay together, I think they're sick of the sight of each other! They've been in every day together working hard.
"They've both had big disappointments but Doc could sneak in, I don't know."
Glenn Hoddle believes Gary Doherty could 'sneak in' to Ireland's World Cup plans - but suggests he's not quite ready for international football at the moment.