Tuchel led the Three Lions to a semi-final loss against Argentina before going on to beat France in a whirlwind third-place play-off.
Mainoo suffered an injury in training ahead of the France game, and Tuchel admitted he was planning to utilise the Manchester United star against Didier Deschamps' side.
On his return to Manchester, Mainoo has been vital for Michael Carrick so far this season, and Tuchel indicated he will get his chance in the upcoming UEFA Nations League games.
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"I expect him to be on the pitch for these games and it's my duty to put him out there.
"The World Cup was totally on me. He didn't put a foot wrong, he was class in his behaviour and on the training pitch. It was a big competition for places.
"We also played with Reece James in central midfield. Elliot Anderson was fantastic for us. Declan Rice is a very unique player.
"So we trusted them more than we trusted Kobbie. It was difficult for him.
"He was then injured before the France game, so we could not even give him minutes there, which hurt me.
"Maybe he was more hurt than me, but it was my responsibility, and it's my responsibility to reward him for that."