Perez was key to Benfica's success last season, scoring five goals as the Lisbon club won the Primeira Liga, Taca de Portugal and Taca da Liga while also reaching the final of the UEFA Europa League, only to lose to Sevilla on penalties.
The 27-year-old extended his contract until 2018 before linking up with the Argentina squad for the FIFA World Cup.
However, Premier League side United and Spanish outfit Valencia are both thought to be keen on acquiring his services, although the former Estudiantes man insists he is happy at Estadio da Luz.
"I know about their interest, I have heard about these possibilities and my agent told me about them too," Perez told O Jogo.
"There is the possibility of playing for Valencia, who are a great club, but right now I want to be fully focused on the Argentina national team and on the World Cup.
"I am very happy at Benfica, I signed the contract renewal before travelling to join the Argentina squad, which shows that I want to keep wearing this shirt.
"I am feeling very well at Benfica and I know the club will try to do the best for me, I'll respect what they decide."
