Christopher Jullien gave Neil Lennon his total backing after Celtic were knocked out of the Europa League with another 4-1 defeat by Sparta Prague.
The Hoops went into the Group H fixture with one point from three matches, the last of which was a defeat by the Czech Republic side at Parkhead by the same scoreline earlier in the month.
Odsonne Edouard gave the visitors the lead in the 15th minute but defender David Hancko levelled in the 27th minute and then striker Lukas Julis, who notched a hat-trick in Glasgow, scored a brace with substitute Srdan Plavsic adding a fourth in the final seconds.
The nine in a row champions have two wins in their last nine games in all competitions and are trailing Rangers by 11 points at the top of the Premiership, albeit with two games in hand, and the pressure on Lennon is sure to intensify after a section of the Hoops support had called last week for the manager to go.
However, French defender Jullien, returned to the side in the Czech Republic for the first time since September after a back complaint, said: "I have no worries about the trainer because after the game we still believe in each other, we still believe in staff, we still believe in the coach.
"He has our 100% belief in him. He is just a great coach and since I arrived he has done unbelievable work, he was doing it before and he's going to do it again.
"I don't have doubts. We have just to look to each other.
"The staff and the job that the coach is doing is really great. The training that they do for us is just really great.
"I repeat myself but I really think that we just have to believe in each other to get back in the shape that we were in.
"It was a bad night but at the end of the day we still have some big stuff in front of us, a lot of big games and we definitely have 100 per cent support of the staff."
