Celtic defender Jozo Simunovic faces further time on the sidelines after being booked in for knee surgery.

The centre-back has missed the last four games and a trip to see a specialist on Friday has resulted in action.

Manager Neil Lennon told Celtic TV: "Jozo's in for surgery. He's going to have a clean-out in the knee, an arthroscopy it's called."

The surgery is likely to see him sit on the sidelines for weeks rather than months.

Celtic are set to have an unchanged squad for their Europa League group opener against Rennes on Thursday with fringe players Luca Connell and Marian Shved the only players to join Simunovic, Nir Bitton (hamstring) and Mikey Johnston (groin) on the sidelines.

"Nir and Mikey will be more towards the end of the month," Lennon said.

"There are no fresh injury worries from the weekend, just a couple of injured boys in training.

"Luca Connell picked up a slight thigh strain and Marian has a little ankle sprain as well, so they will be out for Thursday."

Despite the absence of Simunovic and more recently Bitton, Celtic's new-look defence has had some encouraging signs in recent weeks with new signings Boli Bolingoli and Christopher Jullien settling into life in Glasgow and Hatem Abd Elhamed fit again.

Celtic have kept three clean sheets in their last five games and Lennon hopes to continue that trend in France along with another one, which has seen his team score in all 14 competitive matches this season.

"I still want the goals," he said. "I still want us to be a threat. I still want us to play with the purpose and penetration that we have shown so far this season.

"It might be difficult on Thursday at times where we may not have the dominant side of possession but the players are well-equipped to go over there and score and pose a threat.

"And that's obviously trying to find a balance between being difficult to beat and being a real threat, not just on the counter-attack but in possession."

Celtic did fail to score in a goalless Parkhead friendly with Rennes in July but Lennon is not reading much into that contest, which featured 23 substitutions.

"They played a back four in the pres-season game but they have started the season in Ligue 1 with three at the back," Lennon said. "They are playing 3-5-2. So it's a total change of formation.

"They have had an excellent start to the season, they beat PSG a few weeks ago. They had a draw at the weekend (against Brest) but looking at the performances they are a very good side, a very good side.

"They won the cup last year and they have obviously built on that. They are a team with a lot of confidence, good energy, technically very good and with a bit of pace as well. It's a big test for us and one we are very much looking forward to."