Pogba was heavily linked with a move away from United to join Real Madrid early the summer after he disclosed that he was ready for a new challenge.
He was keen on a move to the Spanish giants but Real Madrid did not meet United’s £150m asking price.
Speaking with Spanish television El Chiringuito, Mathias reassured that his younger brother would ‘focus’ this season because of United’s lack of ‘great players’.
“Paul knows that he cannot leave Manchester United so he’s going to focus on this season, it’s not easy right now, because he has a lot of responsibility in the team,” he said.
“A lot of big players have left.
“The only great player is [David] De Gea, the goalkeeper, which means he’s going to have to put a lot of effort in every game.”