Celtic fullback Kieran Tierney has admitted to lingering regrets about the manner in which the Parkhead side failed to consolidate a third successive invitation to the UEFA Champions League group stages this season.

Brendan Rodgers’ side will begin their Europa League group campaign this week when they take on Rosenborg at Celtic Park with Tierney determined to make the most of the experience.

“We could have done a lot better, especially in the Champions League and we know that,” he said.

“It was a particularly sore one in Athens because we had the quality to beat them but we didn’t use it which was the most disappointing thing. We are now in the Europa League group stages which is the next big thing for us. We can now look forward to these matches against Rosenborg, Red Bull Leipzig and Red Bull Salzburg.

“It is something different and although it is a disappointment that it is not the Champions League they are still games to look forward to. All three teams are decent sides and will offer us different tests and want to go out and do well and get as far as we can in the tournament.”

For now, though, the immediate concern is on focusing on the game against St Mirren tomorrow night, with Tierney wary of the kick that the arrival of a new manager may bring for the Paisley side.

You always get that bounce with a new manager,” he said. “The players want to do well and will be out to impress him to try and get in his team going forward. It will be a tough game. They did well winning promotion and although they have changed their manager they already have points on the board and that shows they have something about them.

“But, of course, the aim is to get back on top of the table and to stay there as long as possible. It is one game at a time and that is St Mirren. We will be looking to take the three points there and from there to try and go on the sort of run we are capable of.” Meanwhile, Rodgers has revealed that he spent the international break taking an overview of the opening months of the season. It was the most turbulent few months of Rodgers’ tenure at the club with a difficult transfer window - French striker Moussa Dembele moved to Lyon in the final hours of the window - while the club failed to make it through the UEFA Champions League qualifiers. “I normally use a few days of the international break to reflect on the previous round of games,” Rodgers told www.celticfc.net. “It’s been nearly three months so it’s been such a busy period. I like to have thinking time to go away and take stock of everything that’s gone on.

“When you’re trying to be creative as a manager you need that time to reflect. I try to take that opportunity to do that when possible.

“We still have a group of players who have still been here working.”