In a quip that will have critics scratching their heads, the Blues boss told the club's official magazine: "Young players are a little bit like melons. Only when you open and taste the melon are you 100 per cent sure that the melon is good.
"Sometimes you have beautiful melons but they don't taste very good and some other melons are a bit ugly and when you open them, the taste is fantastic."
Sinclair, 18, and defender Michael Mancienne are two rising stars coming through the ranks at Stamford Bridge.
Mourinho appeared to suggest he is particularly impressed with Sinclair. He added: "One thing is youth football, one thing is professional football. The bridge is a difficult one to cross and they have to play with us and train with us for us to taste the melon. For example, Scott Sinclair, the way he played against Arsenal and Man United, we know the melon we have.
"Now it is a question of the best thing for his short-term future because his long-term future for me will be at Chelsea."