The 28-year-old has caught the eye of Rangers manager Giovanni van Bronckhorst, who is eager to strengthen his attacking options ahead of the upcoming Champions League qualifiers.
Alfredo Morelos is recovering from thigh surgery, but he has been heavily linked with a move away from Rangers, with Sevilla and Besiktas the two latest clubs to be credited with an interest.
Colak is reported to be “keen” on a move to Rangers, but Thessaloniki-based PAOK say they will only sell him if their valuation of £2.6million is met by the Ibrox hierarchy.
In the meantime, he has joined up with his team-mates for a pre-season stint in the Netherlands.
Rangers are also weighing up a move for Sunderland’s Scotland internationalist Ross Stewart, although the Black Cats want to tie him down on a new deal and expect him to be part of their pre-season plans.
Meanwhile, Aston Villa have dropped out of the race to sign Rangers midfielder Joe Aribo, according to reports in Birmingham.
The Express and Star claim that Steven Gerrard is not interested in bringing the in-demand Nigerian to Villa Park.
Fellow English Premier League outfits Crystal Palace, Fulham and Nottingham Forest all hold an interest, with newly-promoted Forest the favourites to land his signature if a suitable bid his made.