Saul, a deadline-day loan signing from Atletico Madrid, has not played in the Premier League since being substituted after 45 torrid minutes of his Chelsea debut against Aston Villa last month.
And despite N’Golo Kante being ruled out by Covid-19 and Jorginho named on the bench for the 3-1 win against Southampton, the 26-year-old was again an unused substitute on Saturday.
Instead, Tuchel named Loftus-Cheek in his starting XI and brought on Barkley in the second half.
The Chelsea manager admitted he feared the impact on Saul if he endured another difficult match.
The German said: “He was very, very close to start. In the end I decided against him because I thought to put him in another high pressing match, against an opponent pressing so high in the centre of the pitch, would it be fair to say, ‘Okay now prove it and let’s see if your adaption has gone further?’
“I hesitated a little bit. He does not need to worry. Just work hard and adapt and the chances will come.
“We have only 11 to give a chance. I would like to see it in a positive way.
“If you turn it around of course you have eight players who we didn’t trust today from the beginning. This is a reality. I cannot hide from this reality.”
Loftus-Cheek and Barkley would both have been allowed to leave Chelsea this summer if moves could have been secured.
But they are now back in the first-team picture after impressing Tuchel with their attitude and application in training.
Meanwhile, Tuchel has confirmed Thiago Silva will not be able to play against Brentford upon his return from international duty with Brazil.
The Blues make the short trip across west London on October 16, and Tuchel said: “He will go and then he will play for Brazil and then he will come back on the matchday versus Brentford.
“This is the life of international breaks, this is the situation of international breaks in 2021.
“Like it or not, what can I do? Is it a good solution for us as a club? No. But we cannot hold him back. It is impossible if they call him, he needs to go. Otherwise he gets suspended from FIFA.
“There is no choice and it is something we have to live with.”