Belgium boss Martinez also worked with Lukaku at Everton - and says it is "clear" he must depart Old Trafford
Belgium boss Roberto Martinez believes "it is clear" that Romelu Lukaku has to leave Manchester United this summer.
The 26-year-old endured a difficult second season at Old Trafford and has been linked with a move away.
The likes of Inter Milan have been reportedly showing an interest in Belgium's all-time record goalscorer, who has netted 42 in 96 games since joining United from Everton in 2017.
However, he failed to find the back of the net in his last eight appearances of the season and was not an automatic starter under Ole Gunnar Solskjaer.
Now Lukaku's international boss, who was also his manager at Goodison Park, feels everyone may benefit if the player secures a summer transfer.
"It is clear that he has to leave Manchester United," Martinez told Belgian newspaper Het Laatste Nieuws.
"It would be a good thing for both parties. It is now important that Romelu finds the right club."
Any potential departure for Lukaku could form part of an overhaul of Solskjaer's squad.
The Red Devils finished the season poorly and ended the Premier League campaign in sixth place.
Paul Pogba's future is also in doubt after the France midfielder suggested he is considering "a new challenge".
United's recruitment has so far been limited to the arrival of winger Daniel James from Swansea as a host of other big-names continue to be linked with the club.
There were suggestions earlier in the week that Lukaku's potential move to Inter may have seen Mauro Icardi head in the opposite direction.
The Italian club believed such an option may have lowered the asking price for the Belgian, which they feel is too high, but it is understood United were uninterested in adding a player to the deal.
The Red Devils would prefer a cash deal for the 26-year-old-striker.