O’Reilly told BBC Radio 5 Live he was “a bit shocked and very surprised” to receive a call-up, but also “over the moon [and] buzzing with the news”.
He started off at Manchester City as a midfielder, but his defensive performances have caught the eye of Tuchel.
“At first I found the switch pretty difficult because I have never played there before,” O’Reilly said of his positional change.
“Obviously I have been training there every day, so it has started to get easier. I got a lot of good advice, so yes, I enjoy it. It’s a bit different but I am enjoying it.
“I have never really done that side of the game, one-v-one defending, but every day I am learning and getting better in the position and I am enjoying it.”
When asked if he is pinching himself after coming such a long way in a short space of time, O’Reilly said: “Definitely, but I try not to think about it too much. I try not to let it get the better of me and just stay calm and stay focused.”
O’Reilly explained that City team-mate John Stones was surprised to see him joining up with the senior England squad at St George’s Park.
“He was a bit shocked, obviously, because I wasn’t initially meant to be here with the squad, but yes, it is good to see him, as a familiar face,” O’Reilly said.
