Corry Evans will face a spell on the sidelines after undergoing a minor groin operation.
The midfielder has been troubled by the injury for some time, and after limping out of Tuesday's midweek match at Ipswich Town, the decision was taken for him to go under the knife.
And with Evans is set for a busy summer with Northern Ireland in the Euro 2016 finals in France, it is hoped that he won't be absent for an extended period of time.
"We hope he isn't out for too long," said Lambert.
"I knew he was always going to miss this game, but unfortunately Corry getting injured on Tuesday night has made it worse. So hopefully it is not too long, we'll find out later on what the timescale is.
"The Euros are vital for any player and I'm pretty sure Corry won't be any different.
"You never know, it could be your first tournament, it could be your last, you just don't know what is going to happen. It is great for Northern Ireland to qualify, it is an incredible achievement, and I'm sure he'll want to be part of it."