The 35-year-old, whose contract runs until June 2010, has not ruled out signing another deal, although matching Brazilian Romario's reputed 1,000-plus career goals looks impossible.
"I'll try to carry on as long as I'm playing like this. Knowing myself, it will be a difficult day when I stop," Inzaghi told Sky television after two trademark goalpoaching strikes.
"I try to work like I always have. I know the things that keep me fit. I must say the coach (Carlo Ancelotti) is great because he lets me have a breather when I need it as at nearly 36 I can't train all the time."
The much-travelled striker, who scored his first professional goal for Leffe versus Siena in the third division in 1992, held up a shirt with 300 on the back after reaching the landmark against the same side.
"I prepared it yesterday because I hadn't realised that my first professional goal was against Siena so it was destiny that my 300th would again be against Siena," he smiled.
The former Italy and Juventus forward has grabbed his chance back in the first team having been little used since scoring both goals when Milan won their seventh European Cup by beating Liverpool 2-1 in Athens in 2007.
"My team have given me a great hand. Strikers live for things like this but results like when Milan won the Champions League that evening in Athens offer much more satisfaction," added Inzaghi, who scored a hat-trick in a 3-0 win over Atalanta last weekend.
He picked out Milan's 19-year-old striker Alberto Paloschi, on loan at Serie B side Parma, as a potential successor.
"I see my desire in him. I hope one day I can give him my number nine shirt."
