Pietersen has not played cricket since pulling out of the Auckland Test against New Zealand in March with bone bruising behind his right knee - an injury he first suffered during a training week in Queenstown before that three-match series.
England bowling coach David Saker spoke to Pietersen at Lord's on Sunday and said: "I just asked him if he thought he would be all right (for the first Ashes Test), and he said he thinks he will. It was probably the only answer he could give. He doesn't know - and until he knows he can run around and it doesn't flare up he can't have an answer on that."
Saker added: "He hopes he will be ready. He was really excited about getting ready for the Ashes, but he said he is still not sure."
After a repeat scan on the injury, Pietersen was last month ruled out of the Champions Trophy - which starts on June 6.
He was at that point nonetheless scheduled to resume full training in mid-June, according to the England and Wales Cricket Board, with an obvious intention of being back in time to face Australia again a month later.
There were reports too, disputed by Pietersen himself on his Twitter account, that he may even play his first comeback match for Surrey as early as June 12.
Saker said: "We all hope he will be back for the Ashes, but we are still not sure on that.
"I think the medical staff are on top of that.
"It would be great to get him back for the Ashes. He is a special player."