Brendan Rodgers has stressed he returned to Celtic to push the club on in Europe – and is “very confident” they can sign players who can help him achieve that goal.

Rodgers spoke of the need to improve the strength of his squad and add quality after a late 2-0 defeat by Lazio in Rome on Tuesday consigned them to a European exit. Celtic have now gone 15 Champions League group games without victory, a run stretching back to Rodgers’ first spell in charge.

Luis Palma has been the standout success story of Celtic’s eight summer signings, but they have together made only nine starts between them in five European games. The departure of Josip Juranovic, Giorgos Giamoukais, Jota, Aaron Mooy and Carl Starfelt has made it difficult for Celtic to improve on their previous Champions League campaign, when they collected two points,

Celtic manager Brendan Rodgers braves the cold during training at Lennoxtown.

Rodgers said: “There’s no doubt now that, one, the squad will come down in numbers and obviously we need to add quality. There is no dressing it up, the group lost real quality players in the summer. That’s something that over the coming windows we will look to improve on.”

Celtic made a £40.7million profit last season and fans are calling for more money to be invested in the squad. Rodgers added: “The supporters have every right to demand the highest level. That’s what we demand here also. The club have been so well run for so many years and from a domestic perspective that’s been highlighted in what the club have achieved. I think the next step is the European side and that’s why I came back, to hopefully be able to fulfil that in my time here.

“I felt when I came in here in the summer, with the squad that was already in place from last season, that we probably needed four players. By that I meant four quality players to add to the squad. Now, how the game works, you lose players, and there were players that were earmarked to come here prior to me coming here. That’s absolutely fine, there’s no problem, we have got young talents here that will develop and grow and that’s the model of the club, but of course to continue to improve and grow you need to also have players who are established because they help bring those players up.

“And I am very, very confident that we can do that over the coming windows. Once we get some of our players back, Daizen (Maeda), Liel Abada, very important players for us, Reo Hatate when he comes back in January will be like a new signing for us. But there’s no doubt we have to add extra quality. We don’t need quantity of players, you need quality and that’s how you improve.”

Celtic crashed out of Europe following defeat by Lazio on Tuesday.

Rodgers added a caveat that January is not the best window to sign new players. Ahead of Sunday’s cinch Premiership game against St Johnstone in Perth, he said: “My sole focus is the players we have and maximising what they are bringing to the game. So far this season, without having a settled team through injuries, the players have performed domestically very well and in Europe they have had some really good moments.

“But the beauty and excitement for me is that I know it will improve and that’s what I look forward to. It doesn’t necessarily all have to be in January because the right players might not be available. It might be the summer, but certainly over my time here we want to improve the depth and quality. If in January we can do that, then I’m pretty sure the club will give us every chance to improve the team.”

Celtic confident of executing 'extra quality' transfer plans but Brendan Rodgers explains January caveat