Australia batsman David Warner has admitted that he 'stepped over the line' in his criticism of Jonathan Trott.

The England batsman has left the squad for the remainder of the Ashes series due to a stress-related illness.

Warner said last week that Trott's performance against Mitchell Johnson in the first Ashes Test was "pretty poor and pretty weak".

"I was always going to cop criticism no matter what from what I said," Sporting Life quotes Warner as saying.

"As I said before, I probably stepped over that line and at the end of the day it's cricket. We've got to go out there and play the best we can and as hard as we can without crossing that line.

"Going into public and saying what I did probably did go over the line a little bit. Obviously it's unfortunate that [Trott] has gone home now. I hope he gets well because we know the type of player he is and he will bounce back from it."

The second Test begins in Adelaide on December 5.