Donadoni also called for three or four targeted summer signings to close the gap on champions Inter Milan.
The former Milan midfielder, who spent a decade at San Siro winning three Champions League titles and six Serie A titles, spoke to La Gazzetta dello Sport ahead of Sunday's match against Atalanta — a fixture that carries major implications for Milan's Champions League qualification hopes with three rounds remaining and only a single-point margin over sixth place.
Donadoni was measured in his assessment of Allegri's contribution and deflected blame away from the manager when asked directly about the team's underperformance.
"The value of Allegri is known and recognised by all. It's the players who take to the pitch who need to have the will and the desire to achieve the objective. A manager can transmit his motivations, but then he stays on the bench and cannot score. I believe Allegri has made the squad grow in terms of performance compared to last season."
He struck a note of frustration about a campaign that appeared to open up as a genuine title challenge after Milan won the derby, only to unravel in the weeks that followed.
"After the victory in the derby I expected Milan to have kept the title race more alive. Instead, old problems resurfaced and the team became less competitive. They lost matches I didn't expect them to lose — against Lazio, Udinese and Sassuolo."
His conclusion was forward-looking rather than accusatory. Three or four signings of the right profile, Donadoni argued, could deliver a meaningful shift in the club's capacity to compete at the top.
"With three or four right additions, Milan can close the gap with Inter and go back to winning."
Milan sit sixth in Serie A with three matches remaining, needing maximum points to guarantee Champions League football. Sunday's match against Atalanta kicks off at 20.45.