The former Manchester United midfielder has impressed this season under Fonseca.
Ahead of their Europa Conference League quarterfinal second-leg with Aston Villa, Fonseca declared: "Angel is maybe the most intelligent player I have in my team.
"He understands faster than the others everything about the game; he loves the game. He loves to learn, and he is a player with big skills, big technique.
"He is a player who, under pressure, finds it is not easy to steal the ball off him and who discovers the space so easily. He is young, he has a big talent.
"I believe with the right coach, with the right project, with the right game for him, he can have the possibility to have a big step in his career."