The midfielder will be a free agent at the end of the season when his contract with Fiorentina expires.
As a result, Milan will not be required to pay a transfer fee to secure his services.
"Next season we will have [Ricardo] Montolivo who is a very good player, very technical," Allegri told reporters. "Milan must remain competitive next season, we must continue the work we started last year. We will start [the season] with great enthusiasm."
The 27-year-old had previously been linked with Arsenal.