On many occasions over the past couple of years the Celtic team has been shared on social media by supporters, who have received it from an unknown source at the club.
This was an issue under Brendan Rodgers and it has continued into Lennon's spell as interim manager.
While the Northern Irishman doesn't believe it's a player in the squad, he stressed the importance of keeping the team under wraps until it's announced by the club around an hour before kick-off.
He said: "I am aware the team does get leaked and I'm really not happy about it. Someone is letting us down.
"I'm not convinced it's coming from a player. I'd like to (change the timing of team selection) but it's what the players have been used to so again I'm not wanting to change too much too soon."