Frimpong shone as the holders crushed Partick Thistle 5-0 at Celtic Park to book a last four showdown with Hibs.
The 18-year-old Dutch youth international joined Celtic from Manchester City on transfer deadline day at the start of this month and was widely expected to initially feature only in the Scottish champions’ development squad.
But the right-back made such an immediate impression on Lennon that he was drafted into the first team squad where the manager now believes he can stay.
“He is battling for a first team place already, no question,” said Lennon. “You can’t stop the talent at times. As soon as he came in, we brought him into first team training and he has excelled.
“We are excited about him but we don’t want to get carried away. For a guy with small stature, he has a lot of personality and energy and strength, he is quite deceptive. It is one game but we feel this guy could be a really good player.
“I thought he was very good tonight. What you saw is what we have seen in training. He took the opportunity to play and he was excellent. We took him off near the end as he was on a yellow card and you worry that fatigue could kick in in the final ten minutes. But he got a nice reception coming off and he can be delighted with his night’s work.” Lennon was thrilled by his team’s display on a night when he made eight changes to his starting line-up but saw no disruption to Celtic’s ongoing success in domestic football as they bid to win a tenth consecutive trophy.
“It’s a nice feeling to see your name in the semi-final draw,” added Lennon. “I know we are so accustomed to it but it’s another cracking game to look forward to. No matter who we got tonight, it would have been a good team with the quality left in the draw. We know Hibs will give us a good game in the league on Saturday too.
“You always want to avoid the better teams, if you want to call it that, but it’s too early in the season to say that. By the time the semi-final comes around, the team you play could be on a great run. But we are in a good position, playing with freedom and looking fit.”