Grealish had trials for England at youth level when he was 15 but ended up hitting his head on a sink and had to be sent home.
Before the next camp came around, Grealish ended up having trials for Ireland.
Grealish told The Sun: "When I was young, I had trials for England. I think I was 15.
"I got there and I was rooming with Diego Poyet, Gus Poyet's son.
"I woke up in the middle of the night.
"I don't know what it was, but I somehow collapsed in the bathroom and hit my head on the sink."
Grealish added that he wanted to stay at the training camp but wasn't allowed to.
After hitting his head on the sink, Grealish was sent home and ended up playing for Ireland at youth level
He said: "Diego woke up and found me. I had to go and get checked out by the doctors.
"The next morning I was completely fine, and I was like, 'Please let me stay, let me stay'.
"But they said, 'No, you need to go home. You can come to the next camp'.
"During that time I had trials for Ireland."