Leao was jeered after Milan's thumping by Udinese on the weekend.
It's been suggested the Portugal could leave this summer, but Serginho told local reporters: "Is it right to say goodbye in June? In football, everything changes quickly, and I wouldn't make any definitive judgments.
"Perhaps Saturday's boos for Leao will be an extra incentive to prove his worth at the end of this season. Sometimes, a single goal is enough to rekindle the flame. For example, if he scored the decisive goal against Juventus."
Serginho added: "San Siro is a demanding stadium that has applauded him many times in the past when he scored and delivered important performances.
"Let's say that in the last season and a half, Leao hasn't always managed to express his great potential."