AC Milan goalkeeper Gianluigi Donnarumma cannot say no if Real Madrid are interested in signing him, according to Antonio Cassano.

Madrid are one of the clubs to be linked with Donnarumma after he rejected an offer to extend his Milan contract beyond 2018, the Serie A club claiming their offer was worth €50million over five years.

The 18-year-old had fake money thrown at him by angry supporters during Italy's match against Denmark at the Euro Under-21 championship last week.

Cassano, who formerly played with Milan and Madrid, offered his verdict on the shot-stopper's future, insisting a switch to Santiago Bernabeu is too good to turn down even if San Siro is the best place for him.

"If I was in Donnarumma's place, I would stay at Milan for a few more years," Cassano said to Sky Italia of the keeper, who has also been linked with Juventus and Manchester United. 

"It would be good for Italian football if he remained in Serie A. 

"But it is true that if Real Madrid are there, you cannot say no."

Meanwhile, Cassano believes his former Italy team-mate Mario Balotelli, who he previously described as overrated, has found his level at Nice.

Reports in France suggest free agent Balotelli – like Donnarumma a client of Mino Raiola – is close to signing a new contract that will extend his stay with the Ligue 1 club beyond the 2016-17 season and Cassano feels that would be a wise approach.

He said: "Balotelli had a good career and he is fortunate to have Mino Raiola as an agent to help him earn a lot of money. I think Nice is the size of club he belongs at."