The 23-year-old agreed to join the Serie A giants on loan from Everton in January and he has upped since leaving Merseyside.
Deulofeu has excelled during his eight league appearances for Milan and he has been rewarded with a call up to the Spain squad for the World Cup qualifier with Israel and the friendly against France.
Lopetegui believes the former Barcelona man was right in his decision to head out on loan and feels he is emerging as an important player once again.
“He is a player that we know very well and that wasn’t playing regularly at Everton,” Lopetegui said. “His move to Milan has once again made him an important player. He is starting in every match and is going through a great run of form.
“We believe that he can continue to grow and help us.”