Nani penned a new five-year contract in September 2013, but has fallen out of favour at Old Trafford, making just 14 Premier League starts in the last two seasons.
The 27-year-old, who joined United from Sporting Lisbon in 2007, could now be set to move on, with the likes of Arsenal and Juventus linked with the Portugal international.
Nani could also return home and is quoted as saying in The Guardian: "I'm a United player but there has been some interest on my behalf.
"I will evaluate it and decide what is the most advantageous for me.
"A return to Portugal? Right now I don't know."
Nani started all three of Portugal's matches at the FIFA World Cup, scoring in a 2-2 draw with the United States.
Portugal failed to make it through the group stages though, finishing third in Group G behind Germany and the USA.