Gabbiadini has six goals in four games in all competitions for Southampton after arriving at the Premier League club from Napoli in January.
"I played with Gabbiadini at Sampdoria and it was an enjoyable time. He was a fantastic player because he is so clever," the Italy international said, via the Daily Star.
"The goal he scored against us was down to belief – he believed the chance would come. But in this league you can't give him space because he will punish you.
"At Sampdoria he would work hard on his finishing, and he is very clinical with his left foot. Can he become one of the leading strikers in the Premier League next season? Sure, why not?
"He's a good player, he's scoring a lot of goals now and next year, if he plays like this, he'll be at Real Madrid."
Gabbiadini was on the scoresheet again as Southampton beat Watford 4-3 on Saturday.