[4] After that, he returned to Bulgaria and played in a tournament for Beroe's youth team and there he was spotted by the Litex Lovech scouts.

[8] He impressed the club, whereafter he received a contract offer, but the move collapsed over his work permit rejected by the British Government, having not played enough international matches.

[9] On 25 August 2012, Popov joined Russian Premier League club Kuban Krasnodar on a three-year contract for an undisclosed fee.

Less than a month later he scored his first brace, putting two goals past Krylia Sovetov and contributing with an assist in a 4–1 home victory.

[14] On the last day of the 2012–13 season, Popov scored the only goal in a vital 1–0 home victory over Anzhi Makhachkala, securing Kuban a European debut in the Third Qualifying Round of the 2013–14 UEFA Europa League and earning them their best ever finish in the top flight at fifth, having the same points as fourth-placed Spartak Moscow.

He captained his team to its first away victory of the season over Russian Premier League newcomer, Tom Tomsk, by contributing with a pair of assists.

Popov was named man of the match for the second time in a row, earning him a spot in Russian premier league team of the week.

He scored his first two official goals for the club on 23 September, in a 7–0 win away to Volga Nizhny Novgorod in the Round of 32 in the Russian Cup.

On 30 April 2017, he provided two assists in a 2–1 away victory over city rivals, CSKA Moscow, which earned him a spot in the Russian Premier League team of the week for matchday 26.

[26] On 28 April 2022, Popov signed a two-year contract with Levski Sofia beginning from the 2022–23 season, thus returning to his home country after 12 years.

[27] On 15 August 2023, Popov moved to Botev Plovdiv from Levski Sofia after terminating his contract, thus joining as a free agent.

[29] On 9 February 2011, Popov scored twice from the penalty spot in a 2–2 friendly draw with Estonia, but the result was subsequently declared void by FIFA and expunged from the records due to suspicions of match fixing with the involvement of the game officials.

In the next official match, he once again proved his worth after the only goal in a tough but decisive 0–1 away win against Malta, keeping the hopes alive of his national team qualifying for Euro 2016.

[33] In September 2010, just days before the Euro 2012 qualifier against England, Popov led a group of teammates out of the training camp in Pravets and took them to Botevgrad so they could celebrate Valeri Bojinov's birthday, where the players consumed large amounts of alcohol.

In September 2011, as Bulgaria was preparing to host England for the second leg of the Euro 2012 qualifier, Popov again led a group of players to a bar, where they drank until 4 am, angering then coach Lothar Matthäus.

[35] Days later, it came to light that Popov had abused and humiliated the national team masseuse on several occasions, forcing him to do pushups in front of the other players.

[36] At this point, the executive committee of the Bulgarian Football Union had seen enough and proceeded to ban Popov from the national team for life.