Liverpool have completed the signing of midfielder Marko Grujic from Red Star Belgrade.
As part of the deal, the 19-year-old will return to Red Star and remain there on loan until the end of the season.
The transfer fee and length of contract have not been specified, but Sky sources understand the fee to be £5.1m.
"I'm very excited and so proud to be here and a member of Liverpool Football Club. I can't wait to get started, play at Anfield and train at Melwood," Grujic told the club's official website.
"I was thinking about my progress in my next period and decided it was good for me to come here and try to be the best I can.
"I want to play in front of one of the loudest set of fans in Europe at Anfield.
Grujic underwent a medical at Melwood before signing the deal
"I also like the atmospheres at other stadiums, the crowds are very good. I like to play under pressure and that's why I've come here - because it brings out the best in me."
Grujic, a Serbia U21 international, was a member of Serbia's FIFA U20 World Cup winning side in 2015.
Liverpool manager Jurgen Klopp said: "We're very pleased because Marko is a big talent and we've seen him a lot of times.
Grujic becomes Jurgen Klopp's first signing as Liverpool manager
"When I came here, our scouts showed me some footage of a very skilled player from Red Star Belgrade. We watched it, we spoke to him, we met each other - he's a good boy, a young boy but plays an important role at the moment at Red Star, who are the best team in Serbia.
"To describe him, I would say he's a tall boy, but quick and good at technical things. He can play passes and can dribble. But he is young, so he has to develop. He will do this, so everything is okay.."
