The 19-year old highly-rated player joined Atalanta’s Serie A side last January for 21million euros (PS18.7 million). Add-ons could make this fee 41m euros (PS36.5m).
Diallo played eight times last season. He was due to join Feyenoord for a season-long loan, but he suffered a thigh injury that ended his chances of joining the Dutch club.
Since returning from fitness, the Ivorian has played only one match for United’s first team. He is now on loan to Rangers, the reigning champions of Scotland.
According to the PA news agency, Diallo is in Scotland at the moment as the temporary switch gets closer.