Italy international Balotelli is on the verge of an estimated £16 million switch to the Premier League runners-up, and was photographed at the club's Melwood training ground on Friday evening, UK time.
He is expected to hold talks with Liverpool manager Brendan Rodgers and undergo a medical over the weekend.
Liverpool face Balotelli's former club Manchester City on Monday, though the 24-year-old will not be able to play, even if signed ahead of the clash.
Jackson Martinez is thought to be top of Milan's wishlist to replace Balotelli, having scored 61 goals in 93 games since moving to Portugal from Jaguares in 2012.
But Porto president Pinto da Costa is insistent the Colombia international will remain at the Estadio do Dragao.
Gazzetta dello Sport quote Da Costa as saying: "Jackson is incredible, we will not be selling the striker."
Balotelli's impending signing at Anfield will help fill the void left by Luis Suarez's departure to Barcelona, joining Rickie Lambert, Adam Lallana and Lazar Markovic in boosting Rodgers' attacking ranks.
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