Lennon is trying to minimise the growing hype about Forrest, who is seen as a long-term replacement for the departed Aiden McGeady, but feels he has no option but to promote the 19-year-old midfielder to first-team duty.
Forrest scored Celtic's third goal in a 4-0 success over St Mirren which also saw Joe Ledley, Shaun Maloney and Ki Sung Yueng find the net.
Lennon said: "I'm trying to keep a lid on the kid, not banging the drum but trying to play it down, but I couldn't keep him out of the team any longer.
"He was ready to play and I think everybody saw today how good he can be. It's a great start to his career.
"Everything you do, you try to do positively. He's an exciting player with an eye for goal.
"He's an old-fashioned winger who just wants to hurt people. He looks like a kid that's come in off the street and said, 'Right, throw me a ball, I'm ready to play'.
"I love his attitude and he's a breath of fresh air."
Lennon pronounced himself well satisfied with Celtic's fluent dismantling of St Mirren with a four-goal victory margin that could have been twice that on the balance of play.
He said: "We got a clean sheet and some of our football at times attacking-wise was breathtaking.
"We have got energy in the team and we've got quality. It's all right me asking them to do it, they've got to take it on board.
"You can't play like that all the time, but in certain games you can and the crowd responded to the players.
"It was important to go to Utrecht with a good result because it's a big game in the context of the season and we'd like to get a European run going."
Lennon added that Glenn Loovens, linked with a possible move away from Celtic, had not been dropped, but was absent because of a hamstring strain.
St Mirren manager Danny Lennon struggled to find any positives from his own team's display and admitted his game plan disappeared as soon as Ledley opened the scoring.
He said: "We certainly caught them on a very good day today. Everything we spoke about prior to the game, we ended up doing the opposite.
"We gave them the dream start in the first five minutes and that gives, not just their players, but their fans a lift.
"We tried to go out with a game plan to frustrate them and try and get the crowd on to them, but that didn't happen.
"The players aren't going to come up against this quality week in, week out. They're a quality side that move the ball with a tempo and from a footballing point of view it was thrilling to watch even if it wasn't nice to be on the end of it."