Niall McGinn faces a battle against time to be fit for the start of the new season and force his way into manager Neil Lennon's plans.
The winger suffered a metatarsal injury at the end of last season and will be working on his fitness while the rest of the squad are on their pre-season tour of North America.
McGinn, 22, is gutted to miss out on the trip but will focus instead on being back in action for the games that matter when the campaign gets under way for real.
He said: "It's disappointing. It happened in the last training session of last season so I didn't have the best of summers.
"But thankfully I got the all-clear last week so it's just about progressing from here. I should be back training in four to six weeks and hopefully I'll be back for the start.
"It's going to be hard but I just need to make sure that I'm coming back fit and healthy."