Diallo, 24, found the net 12 times in 24 Ligue 1 appearances this season and also provided three assists.
Last season, he scored an impressive 26 goals in 37 games to help Metz win promotion back to France’s top flight.
But his agent Thierno Seydi told the APS that Metz can expect to lose their star striker before next season.
He also confirmed that Jose Mourinho’s Tottenham Hotspur had made a bid in January.
“Already in January, there was an offer from Tottenham,” Seydi said.
“Now he has received an exit slip and as soon as the European markets open, he should settle [a move].”
Diallo will not be short on interest, although it remains to be seen if Spurs come back for him.
Diallo is a Senegal international, having made his debut as a 55th minute substitute for M’Baye Niang against Equatorial Guinea in 2018.