According to latest reports, an agreement has been reached between the two clubs and the confirmation is only a matter of time. The player is heading to Istanbul to finalise the personal terms and will sign a contract with the Turkish club after the medical is done.
The report adds that Omeruo has already said his goodbyes and the transfer is virtually complete.
The 22-year-old defender had a very good season on loan at Kasimpasa last year and has attracted a lot of interest from other Turkish clubs. The Nigerian defender made 25 league appearances for Kasimpasa last season, who finished 12th in the Turkish top flight.
Omeruo is yet to make a first team appearance for the Blues having arrived from Standard Liege in January 2012. The player has spent most of his time out on loan at ADO Den Haag and Middlesbrough.
Besiktas have been looking at centre backs this summer and were linked with a move for the Liverpool centre back Martin Skrtel. The Slovakian has joined Fenerbache instead.
Omeruo is in the penultimate year of his Chelsea contract and is unlikely to get any more chances of proving his worth at Stamford bridge.
The reputed Turkish outlet TRT Sport also confirmed the agreement between the two clubs earlier this month.