Chief executive Peter Lawwell joined Celtic's first team at Lennoxtown following the departure of Neil Lennon.
The Parkhead boss' resignation was officially confirmed on Wednesday morning with assistant John Kennedy placed in interim charge.
A dismal weekend defeat to the Premiership's bottom side Ross County proved the end of the Irishman's reign.
Kennedy will take training as the team prepare for Aberdeen's visit to Glasgow 18 points behind champions-elect Rangers.
Attention at boardroom level will turn to appointing the next permanent manager.
Lawwell, who himself will leave the club in June, was pictured arriving at the club's training base this morning.
Captain Scott Brown, who could take up a coaching role, was also among those snapped at the gates.
Announcing his resignation, Lennon thanked the players for their efforts despite a disappointing campaign.
He said: “We have experienced a difficult season due to so many factors and, of course, it is very frustrating and disappointing that we have not been able to hit the same heights as we did previously.
“I have worked as hard as ever to try and turn things around, but unfortunately we have not managed to get the kind of run going that we have needed.
"I have always given my best to the club and have been proud to deliver silverware to the Celtic supporters. The club will always be part of me. I will always be a Celtic supporter myself and I will always want the best for Celtic.
“I would like to thank so many people at the club who have given me so much and I would also like to thank my family for their love and support. I wish the Celtic supporters, players, staff and directors nothing but success for the future.”
