Felix is considered as one of the top young prospects in European football and the 19-year-old has been linked with several high-profile clubs including Liverpool, Manchester City and Real Madrid.
Fernandes, meanwhile, has a €100 million (£85.8m) release clause in his deal with Sporting and reports in Portugal have claimed that United have already opened talks about a potential deal this summer.
Felix has been hailed as Portugals best prospect since Cristiano Ronaldo and while Mourinho has dismissed that comparison, the former United manager believes both players could make the grade at Old Trafford, or any top club in Europe.
I think they should leave them alone and not talk about Cristiano, Mourinho said at the ANTF Coaches Forum in Portimao.
Its ridiculous to talk about Cristiano and compare the talent that comes up with him, no matter how big they are.
And remember, they are two great talents.