Liverpool have reached a deal with Benfica to buy the Uruguay striker Darwin Nunez for an initial 75 million euros.
Porto needed only one point in Lisbon to wrap up the title in the second-to-last round, and it was able to add to its championship celebration with a victory at its top rival.
Liverpool raced into an early 2-0 lead in Lisbon last week before Darwin Nunez pulled a goal back for Benfica.
Jose Mourinho's Manchester United will be looking to maintain their robust start to their Champions League campaign.
Manchester United's Champions League encounter with Benfica on Wednesday represents a resumption of hostilities with foes.
Mexico forward Raul Jimenez scored a 75th-minute winner and Benfica moved closer to its fourth straight Portuguese league title by defeating Rio Ave 1-0 on Sunday.