The Milan coach is uncertain on whether or not he will be able to bring the Brazil international back to San Siro, but has admitted that he is excited by the prospect
The Brazil international spent six years with the 18-time Serie A winners before joining Real Madrid in 2009, where he has enjoyed mixed success.
"It is difficult to speculate on the percentage for Kaka, but as a coach I look at this issue with great interest," Allegri told Rai Sport.
The 45-year-old also spoke about bringing lifelong Milan fan Mario Balotelli to the club, as well as the possibility of making other signings.
"Balotelli is a Manchester City player, and I have not spoken with Roberto Mancini about him, and I think he still has continuing and important qualities," said the former Cagliari coach.
"I do not think there is the need for reinforcements in defence: Mexes' [own-goal in Sunday's Serie A win over Bologna] was a simple accident, which occurred after a positive performance, and we have many good players in that department.
"I think a coach, like a business leader who has people under him, needs to know how to wait patiently for the results of the work."