The Portugal international is about to enter the final year of his contract at Old Trafford and no extension has been put in place.
It has been suggested that United would be willing to sanction a sale when the transfer window re-opens, while Nani is said to be open to the idea of taking on a new challenge.
He is, however, keeping his cards close to his chest when it comes to speculation regarding his future.
Nani has been linked with a number of clubs in the Premier League and across Europe, but he has refused to rule out the prospect of remaining at United.
He said: "My future? Nothing is certain.
"I am calm. I have everything in my hands.
"I am not saying that I will not continue at Manchester United. I will think about what is best for me."
While remaining coy on what his decision will be, Nani has ruled out a return to his homeland.
The 26-year-old winger added: "I have respect for the Portuguese clubs, especially Sporting Lisbon but also Benfica and Porto, but I don't think that is viable.
"I think my level at the moment is different."
Nani has also conceded that he would like to play alongside international team-mate Joao Moutinho, who is now at Monaco, but admits that he does not know whether such a switch would be possible.