Lukaku has been linked with a United exit throughout the off-season and the Belgium striker is poised to join Inter before the Premier League transfer window shuts on Thursday.
After months of negotiations and interest from Serie A champions Juventus, who had hoped to agree a swap deal involving Paulo Dybala, Lukaku is reportedly set for a €75.9million (£70m) plus add-ons transfer to Inter.
Lukaku's agent Federico Pastorello confirmed the 26-year-old's imminent switch to Inter via Instagram.
Pastorello posted a picture to social media with the pair on a plane and the caption read: "Ready to take off …. direction Milan!!! @inter… we are coming."
Lukaku landed at Milan's Malpensa Airport on Thursday morning and he was greeted by rapturous Inter supporters.
Belgium international Lukaku, who has acknowledged a desire to play in Italy, scored 12 Premier League goals in 2018-19.
The 26-year-old – contracted to United until 2022 – scored 15 goals across all competitions as United finished sixth in the Premier League and lost to Barcelona in the Champions League quarter-finals last season.
Lukaku is set to leave United having scored 42 goals in all competitions since joining the Red Devils from Everton in 2017.
