Ole Gunnar Solskjaer has warned his Manchester United players there is no room in his squad for those who "fake" it.
United begin the New Year hosting Aston Villa on Friday, where a win will see them go level on points with Premier League leaders Liverpool.
After a poor start to the season, United have turned a corner and are in the title mix for the first time since Sir Alex Ferguson stepped down in 2013.
Solskjaer believes his squad have become mentally tougher as the season has gone on and warned players who go through the motions will not be part of his plans.
Asked if he had seen a real shift in his squad's mentality, Solskjaer said: “Yes, definitely. One, they’re two years older than when I came.
“Two, some of them are really strong personalities that we’ve brought in and they've been a really good influence.
“We have competition for places, which means you cannot go around and think you can just fake your way being part of this team.
“You only deserve to be in a team that you contribute to.”
Marcus Rashford scored a 93rd-minute goal to seal a 1-0 win over Wolves in midweek and Solskjaer said United's ability to go the distance in games will be crucial this season.
“We have to know that so many games are decided towards the end,” said Solskjaer.
“It’s very seldom that you can blow teams away and win by half-time.
“Subs will come on and make a difference - that’s happened so many times for us.”
Following the game against Villa United face rivals Manchester City in the Carabao Cup semi-finals on Wednesday as they bid to reach a first major final under Solskjaer.
