On 13 August 2011, in the second league game of 2011–12 season, against Chernomorets Burgas, Popov ruptured his anterior cruciate ligament and received surgery a week later.

On 26 July 2012, he scored his first-ever European goal in a 1–1 home draw against Slovenian side ND Mura 05 in the Second qualifying round of 2012–13 Europa League.

On 8 March 2014, Popov again played as a goalkeeper for a few minutes in the 1:0 win over Levski Sofia after Raïs M'Bolhi had been sent off in the closing stages of the match.

[10] He made his debut in the game on 11 August, coming on for the last 7 minutes in place of Chavdar Yankov as Bulgaria loss 1–0 at Dinamo Stadium in Minsk.

[11] Three years later, on 9 September 2014, in Bulgaria's first match of UEFA Euro 2016 qualification, Popov made his competitive debut in a 2–1 victory away to Azerbaijan at Bakcell Arena, Baku, playing full 90 minutes in the centre of defence.