There are already four left-backs on the books at Stamford Bridge and the return of Chilwell is a huge positive for the new season.
However, Tuchel does not necessarily see Cucurella as competing with the England man for a starting spot.
"Marc is an option at left-back but he can also play well in a back three," he said before Cucurella's arrival was announced later on Friday. "He fits the profile that Cesar Azpilicueta does, just with a left foot. It gives us many options.
"Ben is hugely ambitious as always but this signing will help him escape the pressure of having to deliver and us needing him now.
"This is a very demanding league and it is our responsibility to take care of him and not just throw him in. "
Chilwell only made seven appearances last season but still supplied three goals and one assist from his rampaging wing-back role.
"He needs time to adapt to the rhythm of matches - which is absolutely normal," said Tuchel.
"Still, we will try to get him on the pitch as soon as possible because he is a huge asset for us on the left side with his speed and intensity."