The Bosman signing from Toulouse has managed 13 appearances for Los Che so far this term.
Mathieu said: "Compared to France, football here is more complete, faster and more technical.
"What surprises me most is that here all the teams try to practice good football and to move the ball cleanly. Moreover, here I am forced to sacrifice myself a little more than in France for the needs of the team.
"I must indeed be tougher defensively and make my attacking runs with more restraint."