Liverpool are expected to announce their first signing under Jurgen Klopp on Monday.
Marko Grujic will become the first new arrival at Anfield under the German manager when he completes his £5.1m move from Red Star Belgrade.
"On 4th January I will become a Liverpool player," confirmed the 19-year-old in a post on his Facebook account.
However, the Serbia U21 international will be loaned straight back to the SuperLiga leaders for the remainder of the season under terms of the transfer.
Red Star, who have a 25-point title lead and are unbeaten in 22 league matches, confirmed the deal in a statement on their website before Christmas.
"In the last 10 days we have received three formal offers for the transfer of our player Marko Grujic: from Anderlecht €2m, Stuttgart €5m, and from Liverpool we received an offer worth €7m and 10 per cent of the next transfer," said the club.
"All in Red Star sincerely want Marko Grujic to stay for the next 10 years, but the financial situation of our club dictates the adoption of a different decision.
"The board considered the offer and unanimously accepted the offer of the English giants.
"Liverpool will pay the money immediately, and the player will stay in Red Star until 01/07/2016.
"We wanted to respect the desire of the player's father Marko Grujic remain until next summer at our club and we agreed to pay Liverpool €1m for the loan of six months."