Besiktas will not allow Wout Weghorst to join Manchester United unless they are able to bring in a replacement.
The deal is close to completion, after the Turkish club agreed to receive £2.5million in compensation.
Weghorst has been on loan at Besiktas from Burnley, but there is no break clause in the deal.
However, having accepted United’s offer, Besiktas want to bring in another striker before they rubber-stamp Weghorst’s move.
Besiktas are being linked with Vincent Aboubakar, who was forced out by Al-Nassr so the Saudi Arabian club can create space in their foreign quota to sign former United forward, Cristiano Ronaldo.
Weghorst has enjoyed a fine campaign so far, scoring nine goals in 18 appearances for Besiktas.
The 30-year-old previously played in the Premier League with Burnley, scoring just twice as they were relegated last season.