The veteran midfielder moved to Sunderland in August from Bayer Leverkusen, but only after Juventus pulled out of negotiations.
Tuttosport says Juve management now regret their decision - particularly given his impact with Sunderland upon their Premier League return this season.
Xhaka's form has Juve now preparing a new move for the Swiss ahead of the January market.
For their part, Sunderland have little interest in parting with their captain, though Juve believe they can bring them to the table with an offer of €20m.