James has sustained a number of injuries in his career and claimed over the past week that talk over his chances of staying fit is “so boring”.
"I've been fit for a long time before my last injury, and I don't listen to too much noise.
"I just focus on myself and my body, trying to perform the best I can and help the team I'm playing in,” James said.
The Chelsea star has not looked his best at the World Cup so far, failing to impress in an underwhelming England side in the Group Stage.
Speaking to Bet St George, Johnson says he understands why James isn’t playing at 100% as he holds back under manager Thomas Tuchel.
“I think Reece James is holding back and it’s totally understandable. If your body keeps breaking down, it is hard to push it to the limit when you aren't confident. It would be a horrible feeling, so you can understand why he might play with the handbrake on to avoid losing another six weeks to injury.
“The good thing is that he is intelligent enough to recognise that. I still believe he is our best right-back, even if he can only provide glimpses of what he used to do.
“Most players go through a stage like this, if you have just returned from a hamstring injury and had a similar issue a couple of months prior, that first sixty-meter sprint is mentally very difficult. You can totally understand his caution, but I think he still has plenty in the tank.
“He can be sensible by choosing his moments to attack rather than joining every single one. By being selective about when he tries to be dangerous, he can reserve fuel and protect his body.
“If we can have Reece James at 75%, we’ll certainly take that.”
James is set to start in the final Group Stage game against Panama this weekend as fans monitor his progress this summer.