The striker, who has been absent from the first-team as he battles off-field issues, posted a picture of the two on his Instragam account along with three raising hands emojis.
He also included a few egg-timer emojis, suggesting the 28-year-old can’t wait to get back and play for his former boss.
Lennon originally brought Griffiths to Parkhead in January 2014 before the Northern Irishman left the club the following summer.
Griffiths would become a Celtic star under successor Ronny Deila and continued to star for Brendan Rodgers.
However, he has battled injury and personal problems this season, scoring just six goals to this point.