Karius, who has made 49 appearances since his £4.7m arrival from Bundesliga side Mainz in 2016, lost his place as Liverpool’s first-choice goalkeeper after the club paid £65 million for Alisson last month.
Sources say the initial loan fee is worth £2.25m and that Liverpool would be due another £7.25m if certain performance criteria is met — such as Karius reaching a number of appearances at Besiktas and the Turkish side qualifying for European football.
Liverpool also have a 20 percent sell-on clause if Karius’ switch to Turkey becomes becomes permanent.
The German is still present with the Liverpool squad for Monday night’s game at Crystal Palace, a source confirmed. Simon Mignolet is also with the team in London.
If the loan move is finalised, sources say Karius is expected to sign a one-year contract extension at Liverpool — with the option of a second year if he returns to Anfield for the 2020-21 season — as his current deal expires in June 2021.
Mignolet, therefore, is now expected to serve as Alisson’s understudy, with Liverpool believing the Belgian’s professionalism and Premier League experience made him the better candidate to serve as No. 2.
Even before the arrival of Alisson, Karius faced an uncertain future at Anfield following his performance in the Champions League final defeat to Real Madrid.
The 25-year-old committed two errors that directly led to Real goals in Kiev, although it was later discovered that he suffered a concussion early in the second half before his mistakes.
He returned to Liverpool this summer for preseason, but faced heavy scrutiny and committed another error during a friendly with Tranmere Rovers.
Earlier this summer, Mignolet failed to agree personal terms with Fulham, sources have told ESPN FC, which led to the newly promoted Premier League side signing Fabri from Besiktas. Liverpool then rejected a loan offer from Besiktas for Mignolet as they were only willing to sanction a permanent departure this summer.
The 30-year-old had drawn interest from Napoli and preferred a move to Carlo Ancelotti’s side, but sources say Liverpool never received an offer from the Serie A side, who were reluctant to meet Liverpool’s asking price and hand the shot-stopper a long-term contract.
Napoli ended up sealing a loan for Arsenal’s David Ospina, whom Besiktas had also targeted before settling on Karius.
Besiktas have a Europa League playoff-round match at Partizan Belgrade on Thursday.