James Forrest insists Celtic will get better still after beginning their Champions League qualification campaign with a 3-1 win over Sarajevo.

The convincing victory in the first leg of the opening qualifier at the Asim Ferhatovic Hase stadium on Tuesday night put the Hoops into the driving seat for the return game at Parkhead next week.

The Scottish champions take on French side Rennes in a friendly at Parkhead on Saturday as Neil Lennon looks to build on fitness after a short pre-season break for his squad and Forrest believes another week's fitness work will be a "massive" benefit.

The Scotland international said: "I think some of the boys were back two-and-half weeks and other boys 10 days before Tuesday night.

"A lot of boys got good game time. There is another game on Saturday before next Wednesday so we are only going to get better.

"It was a quick turnaround but you can look at it in a positive way that you didn't maybe need to do as much pre-season training, 10 days and straight back into competitive games. You can make it a positive."

During a rain-lashed night in Bosnia and Herzegovina, the Hoops fell behind in the 29th minute to a Mirko Oremus goal after failing to defend a corner but 20-year-old attacker Mikey Johnston fired in a wonderful strike from 25 yards for his first European goal six minutes later.

French striker Odsonne Edouard put Celtic ahead with a classy goal in 51st minute before substitute Scott Sinclair added a third with a backheel finish four minutes from time as the visitors dominated the second half.

"We are in a strong position," said Forrest, who still believes there is work to do in the return game at Celtic Park.

"It maybe took us a wee while to get into it the game, the first competitive game of the season.

"Once we went a goal down that's when we really started. Mikey scored a great goal and we had a couple of chances before half-time and we got the goals in the second half.

"We took a wee while to get started but once we did, we finished strong. But we are not stupid enough to rule out the return game now.

"We know we need to make sure that we are at it and put in a good performance and be strong into the next round."

Forrest is confident Celtic fans can look forward to seeing more magic from former academy player Johnston.

He said: "He came into the team more at the end of last season and he is a real threat.

"The manager likes wide players and attackers being really positive and that's what he gives us.

"He did well with his goal and hopefully it will give him the confidence to keep going."