Ronny Deila believes having a fit Charlie Mulgrew at his disposal feels like having a new player.

Mulgrew missed the second half of last season with a knee injury and spent five months sidelined before returning to full fitness at the end of the campaign.

He featured for Scotland in the European Championship qualifier against the Republic of Ireland in Dublin and was back for pre-season training with Celtic fully fit.

Deila has pinpointed him as being one of his most influential players and, as the Parkhead club strive to make it into the group stages of the Uefa Champions League, the manager has backed Mulgrew as being one of the players to lead by example.

“It is like having a new player again, having Charlie back,” said Deila. “He is so important for us. It is not just his experience and ability, but he is a big player for us to have in the dressing room.

“He was out for so long and now that he is back and fully fit we know we can rely on him. He can also play in different positions which is important. He is a solid professional.

“Charlie and Scott Brown are two massive players for us and when they are both fit and available we are a better team.”

Celtic head off to Spain this afternoon to play SD Eibar in a friendly tomorrow evening in the Basque country.

It is another encounter Deila believes can assist Celtic in their preparations, but with the return leg against Icelandic side Stjarnan taking place next Wednesday, the Norwegian will make changes to the team that triumphed 2-0 on Wednesday night.

However, while he will rejig things with an eye on the second leg of the Champions League qualifier, he has called on his players to take the game seriously.

“It is a game where we will change things about a little bit, but I want to take a strong team and treat it as an important game,” he said. “We want to get another good performance in before we play the second leg against Stjarnan.

“We know there is still work to be done when we go to Iceland next week, and it is important we are in the right frame of mind for it.

“Playing games like this is always a bit difficult in terms of tempo and pace because there can be lots of changes throughout the 90 minutes but it will give us a good workout. It is playing games that will get us the match sharpness we need.

“I think we should feel confident going to Iceland, but certainly not complacent. There were lots of counter-attacks on Wednesday and I don’t think we were tested too much against them.

Meanwhile, Deila has admitted Leigh Griffiths cut a frustrated figure in the aftermath of Wednesday’s game.

The striker missed a penalty after being involved in a spat with Stefan Johansen over who would take the spot-kick and, having started the game on the bench while Nadir Ciftci took a starting jersey, Griffiths did not look best pleased as he left the pitch.

It remains to be seen whether or not Deila will use Ciftci as his preferred striker, but insists Griffiths has a key role to play.

“He was a little bit annoyed and frustrated afterwards,” Deila said. “I think he was disappointed about the penalty, but it is going to be a long season.

“He has worked hard over the summer. He has lost some fat and put on muscle and he has the ability to pick up from where he left off last season.”