Ireland made a return to action after a lengthy spell on the sidelines in the FA Cup defeat to Coventry last month and was then handed a surprise start at Manchester United in the Premier League.
The 31-year-old midfielder has been absent since, but Lambert feels Ireland could return to contention for the Potters' next match at King Power Stadium.
"He's got an injury at the minute, Stephen, he's hurt his calf," Lambert told reporters.
"He's had a horrendous time with his leg break and all sorts of injuries - he's had some terrible bad luck and he's had another one so that's the reason he's not featured.'
"It's a big, big ask for someone who has been out for two years to get thrown into the fray of this but I think the main thing is for him to get back fit.
"He played well at Old Trafford and had a couple of chances. Adrenalin will take you through the game, although I know he played at Coventry in the previous week."
He added: "The main focus for him is to get fit, whether he'll be fit by the end of this week or next week I'm not sure. The physios will keep on top of it."