Tuchel started the Aston Villa midfielder ahead of Real Madrid ace Jude Bellingham on Thursday night.
The German later explained, "It is normal, but he's one of the best mates of Jude, so I don't think he feels that kind of pressure.
"They compete at the moment for the same position and they're still friends. They are very respectful with each other and like each other. Morgan deserved to stay on the pitch because he had three fantastic performances with him and second of all we didn't know what was coming if our plan was right with the high press.
"It would be unfair for Jude to try figure everything out because we changed our way of pressing in the last two camps. Declan (Rice), Morgan (Rogers) and Harry (Kane) did it already in three-four matches together.
"I figured they could adapt a bit quicker. Once we see the formation we can give clear instructions to Phil and Jude and bring them from the bench."
On Phil Foden's display, he added: "Phil is in good shape and Phil can make any team better in an offensive position.
"In a central position that is my belief and my trust - he is all smiles. He is full of confidence and you see it in the first touches and the movement."