During a training game against the first team, as soon as Manaj saw that the goalkeeper Júnior da Costa went wide, he tried to catch him by surprise with a shot from the middle of the field.

A few weeks later, when Genovese team faced Siena primavera, Manaj made the same effort, but this time the ball ended straight into the net.

[7] After many speculations about his future which related him with teams like Juventus, Atlético Madrid, Roma, on 14 July 2015 Manaj was sold to Inter Milan for a fee of €1 million and he signed a five-year contract.

[10] He made his Serie A debut on 23 August 2015 in team's opening match of 2015–16 season, replacing Brozović in the 85th minute of the 1–0 home win against Atalanta.

[11] On 15 December, Manaj started for the first time during the Coppa Italia encounter against Cagliari, playing full-90 minutes and providing the assist of the first goal scored by Palacio in an eventual 3–0 win.

[13][14] He finished his first season with Inter by making six appearances between league and cup, as he meanwhile contributed in the reserve team's success in Coppa Italia Primavera.

[16] On 11 July 2016, Manaj was sent on loan at fellow Serie A side Pescara along with Cristiano Biraghi as part of the transfer of Gianluca Caprari to Inter in 2017.

[24] On 18 January 2017, Inter Milan confirmed via its official website that Manaj joined Serie B side Pisa on loan until the end of 2016–17 season.

[32] On 1 July 2018, Manaj joined another Segunda División side Albacete on a one-year loan deal with obligation to make it permanent.

[39] On 29 January, Manaj trained for the first time with Barcelona senior side,[40] and on 14 February, he was called up by coach Quique Setien for the league match against Getafe at home, becoming the first ever Albanian to make it to the club's first team.

[48] Manaj received his first international call-up in the Albania under-19 team by the coach Altin Lala to participate in the qualifiers of 2015 UEFA European Under-19 Championship.

[49] He made his debut in the opening match against Denmark on 12 November 2014, playing as a starter in a 1–0 loss where he substituted off in the 60th minute for Esad Morina.

[52] Manaj was called up for the first time to the under-21 squad by the coach Skënder Gega for the opening 2017 UEFA European Under-21 Championship qualifying match against Liechtenstein on 28 March 2015.

[57] Manaj returned to the under-21 side after two years absence in March 2018 for the double 2019 UEFA European Under-21 Championship qualifying matches versus Slovakia.

[65][66] Following Euro 2016, Manaj was called up for the friendly against Morocco and the opening 2018 FIFA World Cup qualifying match against Macedonia on 31 August and 5 September.