David Moyes is keen on bringing Baines with him from Everton to United, but has already had a £12million bid rejected.
Reports in recent days though have suggested that the Scot is lining up a new joint bid for both Baines and Marouane Fellaini.
If that move came to fruition, Buttner’s playing time would be greatly reduced, with Patrice Evra already ahead of him in the pecking order at left-back.
Besiktas are therefore said to be monitoring the situation, as they look to improve their squad in order to bridge the gap in Turkey between themselves, Fenerbahce and Galatasaray.
Emmanuel Adebayor and Jermain Defoe have also been linked with the Turkish side in recent weeks.
As for Buttner, the 24-year-old has appeared just 13 times for United and has so far failed to pick up an international cap for Holland, despite representing his country at U20 and U21 level.
He signed a five-year deal on his arrival at the Theatre of Dreams in 2012, following 119 appearances for Vitesse Arnhem.
It is thought that around £4.4million would be a reasonable price for Buttner.
[cat_link cat=”manchester-united” type=”grid”]