Celtic manager Neil Lennon has suffered an early-season blow after summer signing Gary Hooper was ruled out for up to six weeks with a calf tear.

The 22-year-old sat out the opening Scottish Premier League victory over Inverness Caledonian Thistle on Saturday after suffering the injury during a pre-season friendly against Blackburn Rovers.

The former Scunthorpe striker will now miss Celtic`s Europa League play-offs against FC Utrecht and their opening group game should they progress.

Hooper also looks set to miss SPL matches against St Mirren, Motherwell and Hearts while he will face a fight to make the following contests against Kilmarnock and Hibernian.

The injury to Hooper's left calf has disrupted a promising start to his Celtic career following the forward`s move from Scunthorpe for around £2million.

The Essex-born frontman netted in his first pre-season game against Lyon before marking his competitive debut with a goal against Sporting Braga in the Champions League.

Lennon had high hopes for the striker, who struck 50 times in two seasons for the Iron.

The manager`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.