AMID the bitter disappointment of their sudden collapse to Fenerbahce on Thursday night, there were some positives for Celtic.

Young Kieran Tierney performed encouragingly at left back against some formidable opponents, including Nani and Robin van Persie, on his European debut at the tender age of just 18.

And James Forrest, whose embryonic career has been blighted by injury, also fared well and carved out the opportunity from which Kris Commons scored the second goal in the first half.

The performances of both players in the 2-2 draw against the free-spending Turkish visitors delighted Ronny Deila – but he was pleased with the showing of Forrest in particular.

The Norwegian has revealed the Scotland winger could easily have been lost to the game during his time out of action and predicted he has only fulfilled half of his potential since returning to fitness.

“I haven’t seen him even near to what he is now,” said Deila. “He needed time because he was so long down injury wise. Now he has been injury free for eight months.

“Before, in the games he played he was giving me heartache because we didn’t see the intensity we needed to see. But I know that because he wasn’t fit enough it wasn’t there and also he was afraid to get injuries.

“He had to get over that boundary to understand that nothing was going to happen and he could give 100%. The development he has had over the last month has been tremendous. When he gets 100% in training and in matches then we have a top, top player.

“First of all, it is about trust. We have worked him physically and medically. We have a good understanding with each other. I have been patient. Now we have control of him, but we are not even close to being there. In my opinion he is 50% of what he can be. Now we just have to keep on building, but that takes time.”

Asked if he could have struggled to recover from his injuries, Deila replied: “Yes, of course. The work that the medical staff have done has been fantastic and so important. Also the communication has been so important now between the medical staff and me and that we are always doing what is best for him so we can see the best of James.

“One year ago he was not a happy football player. Everyone talks about potential, but how many times have we seen it? Yesterday you see a player who worked hard defensively and who caused them problems defensively.

“He has balance, speed and technique at the highest level I’ve seen. If you get the other things right and can count on him defensively and offensively. Then you have a very good player. If he continues his development, I’m sure he will be a very important player for Scotland.”

Deila stopped short of saying that Tierney, the youngster from the Isle of Man who has played for the Scotland Under-18 and Under-19 sides, would reach that level. However, he is confident the defender can progress further after handling such an intense fixture with great maturity.

“He has a big future because of two things,” he said. “Firstly, he is gifted in terms of fitness, speed and agility. Secondly he is unbelievably committed to being a top player. He learns quickly and he is curious to learn all the time.

“He is very strong mentally. He is very tight defensively and that’s what I like. We always get full backs now who are very good offensively, but a lot of them lack ability defensively and when you are a defender you are first of all a defender.

“That’s what I really like about KT. He is very rarely caught out of position and he has things to offer offensively. I am looking forward to working with him more in the future.”

The second goal which Celtic conceded at the start of the second half was the latest they have let in at a set piece this season; Fernandao got on the end of a Nani corner and powered a downward header past Craig Gordon.

Deila, though, felt the quality of the move was largely responsible for the strike and not the zonal marking system which he continues to favour at corners and free-kicks.

“I think it was a very good delivery and a good header,” he said. “But again you have to attack the ball and get in front of people when you play zonal defence at a set-piece.”

Celtic are in second place in their section behind surprise leaders Molde – who drew 1-1 with Ajax at home on Thursday night - after two games and Deila admits the forthcoming double header against the Norwegian club will be vital.

He said: “Six points is the goal. Everything is possible, but it is going to be tough. They have started very well and they have confidence.”

Meanwhile, Deila has dismissed speculation linking Celtic with Nigerian striker Leke James of Aalesund. He has also revealed that Charlie Mulgrew will miss the Ladbrokes Championship match with Hamilton at New Douglas Park tomorrow. The utility player will meet up with the Scotland squad on Monday when a decision will be made on his fitness.