The England midfielder arrived from Tottenham in January on what is initially close to a free transfer.
However, each milestone Alli reaches, such as playing 20 games or scoring a certain number goals, will result in substantial payments to Spurs.
The transfer could go on to cost Everton £40 million if Alli is a success.
"I think for Dele it was an opportunity to prove himself and earn a contract," Dunne told Daily Express.
"He's done ok but he's not done enough to start in the team and Everton needs players to start next season.
"So if Alli is going to cost them millions they would be foolish not to look around and see if they can get someone they can trust and they know will be available. He's not proved that over the last six months."
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