The talented attacking-midfielder is already attracting interest from top clubs following an impressive debut campaign with the Portuguese giants.
ESPN says United and Real Madrid have been monitoring his progress with the player likely to be on the move in the summer.
Any side looking to prise him away from Benfica will have to meet his €120m (£105m) release clause.
Felix recently stated: "I'm a professional and very lucky to be well advised. My father was a PE teacher, who was an athletics coach and knows our world very well.
“Then I have the best agent in the world in Jorge Mendes. I am attracted by the big leagues like the Spanish, English, Italian and French. All the best Portuguese players went to play in the most important foreign leagues and, of course, I would like to do it, too."