James faces a race to be fit for England after being ruled out for eight weeks with the knee ligament damage he suffered against AC Milan last week.
In his absence yesterday, Mount stepped up to score both goals as Chelsea won 2-0 at Aston Villa to continue their good start under new manager Graham Potter.
As well as James, Kyle Walker’s World Cup hopes are hanging by a thread due to injury and Tottenham forward Richarlison suffered a scare against Everton on Saturday.
With just over a month until the tournament in Qatar starts on November 20, players face a nervous period with two games a week until the break in the season.
Mount admits the prospect of injury is a concern but said: “As a player you can never think of that because once that is in your mind then things can happen.
“I try not to ever think about not going 100 per cent because I might get injured. I go into every tackle and game 100 per cent but these things happen in football.
“Look, when you have got a massive World Cup coming up you don’t want it to happen but you have got to stay focused in every game you play. It is massively important for us to win games in the Premier League at this stage and you have got to try to stay fit.
“It is difficult and tough, we’re grinding out these games and hopefully when the World Cup comes around you will be as close to 100 per cent as you can be.”
James will not play for Chelsea again until after Christmas and Mount admits he will be a big miss.
“You know what Reecey brings,” said Mount. “He has been absolutely brilliant this season. He stepped up and has been one of the best players in the team.
“To see that happen to him, as a very close friend of mine, is gutting to see. I was absolutely gutted for him. It is a big loss but we have to step up as players. You can see what [Cesar] Azpi[licueta] came on and did today as a captain, he steps up and has a massive performance off the bench and that is what we need from all the players.
“We are such a strong team and we need to step up during these tough periods where we know injuries will happen because of the number of games that we are playing.”
Mount admitted Chelsea struggled without James at Villa Park. He said: “It didn’t feel right in the game. But the most important thing was to be 1-0 up at half-time, then we could take a breather, speak and make a few changes.
“The second half was not as frantic. We had a bit more control. They are always going to have chances, they are at home, throwing everything at us to get a goal and they are fighting for every ball.
“Listen, these games away from home are never easy. When you come away from them 2-0 with a clean sheet then it is exactly what you need.”