Lyon suffered a "significant calf tear" while fielding on day two of a fractious second Test at Lord's, which Australia won by 43 runs to go 2-0 up in the five-match series.

The Sydney Morning Herald and cricket.com.au both said he had been ruled out of the series, with Murphy set to replace him for the third Test at Headingley on Thursday.

Coach Andrew McDonald said the visitors wanted a spinner in their XI to balance their attack in Leeds.

"We like to have a spinner in our attack, it's a different balance, and as you saw (on Sunday) at certain times, we had to do it differently without Nathan Lyon down the other end, which we've been so used to," he told the Herald.

"At times it looked a bit chaotic, so we do like to have that spin option in the attack."

Lyon was quoted by cricket.com.au as saying he did not yet know if he would remain in England for the remainder of the Ashes or fly home for rehabilitation.

"I've been extremely lucky with injuries. I've been around since August 2011 and we've had 126 Test matches and I've played 122 of them," said the 35-year-old, who was playing his 100th consecutive Test at Lord's.

"This is just a little speed bump in the road. This isn't career-defining. I am hungrier than ever to get back out there."

He stressed he would be on hand to guide 22-year-old Murphy if required.

"I sat with Todd in the last session there (on day four) and spoke about spin bowling as we do. I have a lot of confidence in Todd. He is a great kid. He is willing to learn along the way," Lyon said.

"I have told him my phone is always on, it doesn't matter if I am sitting in the changeroom with him or I am sitting at home watching it in bed."

This time last year Murphy was a virtual unknown, before being handed a surprise Test call-up after just seven first-class matches for Victoria.

He grabbed the chance with both hands in a stunning debut against India at Nagpur in February where he bagged a seven-wicket haul in the first innings while bowling in tandem with Lyon.