Ahead of going to Brentford today, Mateta has scored 19 goals in his last 19 games for club and country.
Glasner said: “JP is so confident with playing and scoring goals. He always gets into the situation, and this is the best thing.
“Many ask me: ‘what did you do with JP Mateta?’ And I say: ‘no, he has the confidence now.’ This he showed at the Olympics. He scored goals there and very important goals for France, game-winning goals, and since he came back he shows it again.
“He's always funny, he's in a good mood, but working hard on the pitch so, yes, we are pleased that he's back again.
“He's also in a good mood in the dressing room because he's such a nice guy, and he's one of the first arriving in the morning, one of the last leaving so, yes, again, happy that the squad is together, all the players are fit.”