England boss described the loss to Japan as “painful” after Brighton’s Kaoru Mitoma bagged the winner just 23 minutes into the clash.
Tuchel fielded a starting line-up with 10 changes from Friday's draw against Uruguay in which the Three Lions also failed to win in a 1-1 draw.
Guehi, speaking after the game, revealed that such disappointing gives the England side something to think about heading into the World Cup this summer.
"Obviously disappointing, but we have to be realistic. This is why we play these games towards this time in the season, we need these tests as a team. If we have the right perspective, then these games help us to build, to be better, to improve, and to go into the next stage, which is the World Cup, and to be ready.
"It is important to have these games to see where we are at, but it is all about perspective, making sure we learn, and we stick together.
"It's not easy putting the shirt on. You play against teams that are well-drilled and disciplined. They qualified for the World Cup as well, and they want to prove a point when they come here. I will reiterate, it is important that we stick together, learn from this moment, and move forward."
The final deadline for choosing a 26-man squad is May 30th before England face Group L rivals Croatia on June 17, Ghana on June 23rd and Panama on June 27th in the USA.
Tuchel has a number of months to decide on his side who failed to live up to expectations against both Uruguay and Japan over the past week in what could be a worry for the German.