Striker moves to Dens Park after scoring more than 100 goals for the Parkhead club.
Section of Parkhead crowd booed Griffiths when he was brought on during Celtic's 6-2 friendly defeat to West Ham.
Griffiths won't be with the Celtic squad to take on Lyon, Nice and PSG.
The striker offered advice to those struggling with their mental health as the coronavirus restrictions are set to be extended.
Celtic striker said there was no other place he could put his foot during clash with Sam Woods.
Celtic have complained to Sky Sports over pundit Kris Boyd's criticism of the striker.
The Celtic captain gave his thoughts on the challenge that injured Jeremie Frimpong.
Leigh Griffiths has told Celtic manager Neil Lennon that he is ready for action.