The 23-year-old is in Russia with the Portugal squad for their World Cup campaign.
He is one of a number of players at the Portuguese giants who has cancelled their contract in response to attacks from fans.
Goalkeeper Rui Patricio has already joined Wolves and Martins could be next to head for the Premier League.
He had also interested Liverpool's Merseyside rivals Everton, as well as Arsenal and Tottenham, according to the Daily Telegraph.
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