Celtic striker Gary Hooper is facing up to six weeks on the sidelines due to the calf tear he suffered in pre-season.
The 22-year-old, who moved to Parkhead from Scunthorpe in the summer, sustained the problem in the recent clash with Blackburn.
Hooper sat out Saturday's season-opening victory over Inverness and manager Neil Lennon has now learned the forward is unlikely to feature until the end of September.
He will now miss a number of SPL fixtures and Celtic's Europa League play-offs against FC Utrecht and their opening group game should they progress.
Hooper found the net on his debut in the UEFA Champions League qualifying defeat by Braga following his £2.4million switch from Glanford Park.
A statement on the club's official website read: "Gary Hooper, who sustained a tear in his left calf against Blackburn, could be out the team for up to six weeks."
Lennon's front pair at Inverness, Georgios Samaras and Shaun Maloney, both performed well but passed up a host of chances to make the 1-0 victory more convincing.
Celtic had to rely on Paddy McCourt's wonderful solo effort but the winger is a doubt for the first leg against Utrecht at Parkhead on Thursday.
McCourt suffered a whiplash injury when Maloney ran in to celebrate and Celtic's medical staff are monitoring his progress ahead of the visit of the Dutch side.
Meanwhile, defender Thomas Rogne is out for up to three weeks with a strain in his left thigh picked up while playing for Norway Under-21s last week.
Winger Niall McGinn is progressing well in his rehab from a fractured metatarsal and should have another two weeks to go while Mark Wilson, who suffered a right adductor injury, will remain in rehab for 10 days to two weeks.
Former Motherwell winger Paul Slane ruptured his cruciate ligament in pre-season and has had a successful reconstruction performed in London, but will be out for about nine months.