On-loan at Girona, Maffeo was handed a man-marking job on Leo Messi in defeat to Barca.
Guardiola said today: "I've always said that PL second teams don't compete very well. They need this kind of competition.
"If they can't play in the first team they need to go in other leagues and play in those big games and face players like Messi.
"That's the best way to improve."