Kris Commons has apologised for his angry reaction to being substituted in Celtic's loss to Molde on Thursday.
Commons, who scored in the 3-1 defeat at the Aker Stadion, said the incident was "something that should never be shown publicly on the field".
The 32-year-old's outburst seemed to be directed at assistant manager John Collins and coach John Kennedy.
"I was very frustrated at how the night had gone," said Commons on the Celtic website.
"However, I did not handle this in the right way. My frustration at losing games and my desire to win will never change.
"I know we are all part of a team at Celtic and I am proud to be part of this team. I want this team to win and I am sure we can come together, work hard and get the results needed to qualify from this group.
"I still have every confidence we can do this and in a fortnight we have the chance to make amends [against Molde at Celtic Park]. That's the motivation now for us all.
"I'd like to apologise for my reaction last night, something that should never be shown publicly on the field."
Striker Leigh Griffiths revealed on Friday that Commons had apologised to the rest of the squad.
Deila calls for unity
Manager Ronnie Deila would not confirm if the former Scotland player would be disciplined but, when asked if Commons would be available for selection against Dundee United on Sunday, the Norwegian said: "Yeah, of course.
"It's very important [that Commons apologised] and I'm happy for that," said Deila. "He came to me and did it at once and that's very good. We have dealt with it and now we have to move on.
"We have to have discipline and stay together and he really understands that.
"I've had many of these situations before - it's not the first time. Different sorts of situations as well.
"I'm confident that I have a good relationship with the players. Everybody's disappointed. We have to speak through things and get better."
Deila was also asked about the supporters' frustrations following the loss in Norway, which left Celtic bottom of Europa League Group A on two points - five behind leaders Molde.
"I understand they're angry," he said
"I really understand and I know a lot of people are travelling around with Celtic and have big expectations. We are very, very sorry and disappointed.
"We have to move on and make it good again and that starts on Sunday.
"You will lose football games. This time it was a bad performance, that's why it's even worse to lose. We have to get back on a good performance and the only thing we can do is look forward and do it on Sunday.
"I really believe in what we're doing. The situation is not unbelievably bad. We are top of the league, we are still in both cups, we still have a chance in Europe so there are some positive things."