Manchester City Under-23 defender Jeremie Frimpong has agreed a four-year deal with the Hoops.
The Netherlands Under-19 international told Celtic's website: “It feels amazing to have joined Celtic. What a massive club to be part of. I’m just lucky to have been picked and I’m grateful for everything. I’m just happy to be here and I just want to get on the pitch and show the fans everything that I’ve got.
“I’m looking forward to start training with my new team-mates and getting to know them. They’ve got more experience than me, so I’m hoping they’ll be able to help me as a player.”
Frimpong, who came to Celtic's attention during a match between Celtic and City's Under-23 sides, revealed he had already had a chat with Neil Lennon, who outlined his plans for the 18-year-old.
“The manager phoned me today and told me that he believes in me and he thinks that what I can do will be good for the team,” he said. “That’s really good to hear, and I’m going to try my best to get in the squad and help them to win things.
“My target is to get as many games as I can, to win everything for the team and I’ll give it my all.”
Lee O'Connor also signed a four-year deal ahead of the deadline. The young right-back admitted it was "surreal" to have joined the Hoops but said he was looking forward to getting started after the international break.
He added: "I found out last weekend about Celtic’s interest, and it went from there. Today was a bit hectic but I’m just glad to get it through before the window shuts.
"I’m a versatile player. I can play anywhere across the back four or midfield if needed. I’d say that I’m a wholehearted defender.
"I love defending and tackling, but I like to get forward as well. First and foremost, though, I am a defender.”