"I'm pleased with the transfer and I'm glad that I'll be playing in the Russian championship," Popov told Bulgarian media on Saturday. "No doubt, it's a step forward in my career."
Popov, 24, had agreed terms to join English club Blackburn Rovers from Litex Lovech after completing a medical in August 2010 but the Home Office refused him a permit because he had not played in enough internationals.
The Bulgaria captain, who has scored six goals in 31 internationals, then joined Gaziantepspor. Popov has won the Bulgarian league title, two national Cups and the domestic Supercup with Litex between 2007 and 2010.