Ibrahimovic scored 10 goals in six league games to help the Rossoneri make a fast start to the 2020-21 season, but injuries have hampered him since late November.
Milan have continued to prosper without the talismanic striker, yet Diaz believes the Swede can now play a pivotal role - and not just on the pitch - after making his comeback on Saturday.
The 39-year-old came off the bench in the closing stages of a 2-0 win over Torino, Stefano Pioli's side bouncing back impressively after Juventus had put an end to their unbeaten record in midweek.
"Ibrahimovic is a player who makes the difference," Diaz said in an interview with Sky Sport Italia.
“He transfers his great experience to us. Now that he is back, we will do great things.