The Spaniard has failed to secure a regular first-team spot since sealing a loan move from Atletico Madrid on transfer deadline day.
After the 3-1 win over Southampton, Tuchel told the media: “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.
“I will always do my choices in the best belief for the team and best belief in this moment and for these type of games. There will always be tactical choices and choices of current form and of connections on the field.
“Particularly about Saul, he was very, very close to start today. In the end I decided against him because I thought to put him in another high pressing match, 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’ and I hesitated a little bit.
“I have to take the selection and take the responsibility for the selection and eight players today did not like it. It is also life at Chelsea and we have to keep on going and keep everyone positive.
“The guys have to work for their form because form is most important – form and confidence and a positive attitude. He has everything.”
Chelsea manager Thomas Tuchel has urged midfielder Saul Niguez to work hard in order to force his way into the first XI after a disappointing start to his loan period in west London.
Saul, 26, signed for the European Champions on transfer deadline day but has so far failed to secure a regular first-team spot after difficult matches against Aston Villa in both the Premier League and Carabao Cup.