"Bopara is a good first-class cricketer, but he is not an international cricketer. I think he's got all the talent in the world, but I just don't think he's got the temperament," said Warne, who has 700 Test wickets to his credit.
Bopara scored three centuries in a row against West Indies earlier this summer but the leg-spinner said, "He can be put off his game too easily and he's too worried about how he looks."
"Let's hope England aren't relying on Bopara (for the Ashes) because they could be in trouble," he added.
Warne said England would need the likes of Kevin Pietersen and Andrew Strauss for success in the Ashes.
"Paul Collingwood can be good, but he has to be batting with someone like Kevin Pietersen to bring the best out of him. For England to succeed they will have to bat around Pietersen and the captain (Andrew Strauss)," he was quoted as saying by 'The Guardian'.
The traditional Ashes rivalry between England and Australia starts on July 8.