Premiership clubs Manchester United and Arsenal are linked with the Wales international.
Burley said: “Who is the best left-back around? I was at Chelsea on Wednesday, seeing Ashley Cole play, and Gareth can be better.
“So he can be as good as, if not better than, any left-back around. He’s that good.
“At the beginning of the season, he played one or two games and we took him out for three or four weeks and since then he’s been phenomenal. Gareth is a special one. He has attributes that top players haven’t got.
“Like his quality of free-kicks wide and around the box, which is like David Beckham, really.
“I gave him his debut last year when he was only 16, he played two games at the end of the season because we could see his potential.
“He was expecting maybe 10 games this season but he has surpassed his ambition because of the way he has improved.
“I think virtually every club in the Premiership would take him. I don’t answer the calls though.”