Parma announced Diallo's loan move for the 2020-21 season on social media last week but it was United who secured a deal for the teenager, signing him on a permanent deal that is worth up to £37.2million. He will link up with United in January.
"We worked according to the dictates of the new club, we tried to buy many young players who will be able to give us a hand," Lucarelli told Sky Sports Italia.
"We already had a proven squad, which is strengthened by many interesting young players. You must ask Atalanta about Diallo, we had the agreement and then the negotiation with Manchester United started and they sold him.
"We covered ourselves with other players and we will make up for it, but he would have been useful."