Keane spoke about the midfielder’s struggles for England at Euro 2024 so far.
While Alexander-Arnold does play in central midfield for the Three Lions, he is a right-back at club level.
“When you've been taken off in the two games; that's not a good sign,” Keane told ITV Sport after England's 1-1 draw with Denmark.
“I thought it was always a huge gamble to play him, a player who doesn't play (that position) week in, week out for his club. I know people say he drifts in there for Liverpool, but drifting into a position and starting there are different.
“I've played in midfield, it's a tough position. Physically, getting your distances... He's come up short in the two games.
“Now it's not all down to him. You'd probably have to put this on Gareth (Southgate). It's a huge gamble throwing a full back into the middle of the park. This is not against the French or the Spanish where they have tougher tests ahead. This is against two teams who we thought England would be fairly comfortable against and have lots of possession.
“It was a big ask for him and he's not up to it.”