In June 2016, FCSB transferred Popescu for undisclosed fee, with the player penning a five-year deal with a €10 million buyout clause.

[3] He finally scored his first league goal for the club with a free kick in a 2–0 victory over CFR Cluj on 12 March 2017.

[4] During early April, following Popescu's good display, it was reported that Celtic and Southampton were interested in signing him.

[5] In June 2015, Popescu was selected in Romania's squad for the 2017 UEFA European Under-21 Championship qualifier against Armenia.

[6] He made his debut for Romania national football team on 25 March 2021 in a World Cup qualifier against North Macedonia.