James missed two months earlier this season due to a hamstring injury and was sidelined again with a recurrence of the problem in March.
Since the 22-year-old returned to fitness, Chelsea have looked more composed at the back and carry more threat down the right flank.
Tuchel claims James is so good that he cannot decide whether the England international is better suited to play at right wing-back or right-sided centre-back.
The Chelsea boss revealed deploying James on the right of a three-man defence has not only helped combat opponents in recent weeks, but also contributed to keep his player fresh.
“He can play both positions brilliantly, but we can only select him once,” Tuchel told reporters on Tuesday.
“I think that the back three is a little bit less demanding physically, in comparison to the wing-back position and given that he comes back from a long injury, a re-injury over so many weeks.
“It’s a bit of an advantage to have him in the back-three because it’s less demanding physically.
“This is anyway the next step, how many games can he play as a wing-back, if he plays wing-back during a season, reliable on a level where he’s decisive.
“It’s a bit less demanding physically in the back-three in terms of accelerations, long accelerations and high speed.
“That helps us to have him on the pitch for more minutes, and that’s why he plays in there. So we need to decide, but that’s the reason at the moment.”
Asked which is James’ best position, Tuchel added: “I’m not sure. I love him in both positions I have to say.”
Chelsea host Arsenal in the Premier League on Wednesday as they look to hold off their London rivals in the race for a top four finish.
The Blues sit in third place, eight points ahead of sixth placed Arsenal.
After beating Crystal Palace on Sunday to set up an FA Cup final meeting with Liverpool, Tuchel’s team are hoping for an uplifting end to a difficult campaign marred by the British Government imposing sanctions on owner Roman Abramovich.
However, Tuchel must do without Croatia midfielder Mateo Kovacic, who will miss at least a fortnight with ankle ligament trouble.
“‘Kova’ is out for the game with a ligament injury, and hopefully that will be not longer than two weeks, hopefully,” Tuchel said.
“Two weeks can be a long time for us in terms of games however.”