The winger impressed last season with 14 goals and 12 assists in 42 competitive appearances, while he has already racked up three goals in six Serie A games this term.
Despite starting the season in a positive manner, Leao was linked with a move away from Italy in the summer after Chelsea reportedly had an €80m (£69m) bid rejected late in the transfer window.
While Maldini has previously suggested that the Serie A club would not sell the 23-year-old below his €150m (£130m) release clause, talks have stalled over a new contract.
The former Milan defender has addressed Chelsea's pursuit of Leao, who has two years remaining on his current deal.
As per Fabrizio Romano, Maldini said: "Chelsea haven't sent any official bid for Leão — but they made a verbal proposal... and we rejected, of course.
"He knows that staying here is the best way to improve. We want to do great things with Rafa Leao in our project."
Despite rejecting Chelsea's approach, Milan could come under pressure to sell Leao next summer with Man City believed to be considering a move.
The Portugal international featured in his club's 3-1 Champions League victory over Dinamo Zagreb on Wednesday where he provided an assist for Alexis Saelemaekers's goal.