While the Australia camp have yet to confirm that Lyon is out of the series, they did confirm the severity of the injury following a scan on Thursday night. The spinner arrived at Lord's on the third day on crutches
Nathan Lyon's involvement in the Ashes appears to be over after he was diagnosed with a "significant calf strain".
Lyon, who was playing his 100th Test in succession, sustained the injury in the field on the second day at Lord's. He was immediately helped from the field and arrived at the ground on the third day on crutches.
While the Australia camp have yet to confirm that Lyon is out of the series, they did confirm the severity of the injury following a scan on Thursday night.
"He will require a period of rehabilitation after this match is concluded," a statement read. "A decision regarding his availability for the remainder of the series will be made at the conclusion of the game."
Nathan Lyon has been diagnosed with a "significant" calf strain [Getty Images]
It is unclear if he will be able to bat if required, but there is no chance of him playing any part with the ball.
That is a considerable blow to Australia's chances in this Test. Lyon, who came into the game with 495 Test wickets, looked set to present a significant threat on a dry wicket offering little to the seamers.
Lyon's departure looks set to provide another opportunity to Todd Murphy. Like Lyon, he is an off-spinner, and he enjoyed an excellent start to his career in taking 7 for 124 in an innings on debut in Nagpur.
Aged 22, though, he has little of the experience of Lyon, having played just four Tests and 12 first-class matches.
Lyon's Ashes series could well be over [Getty Images]
Australia have no plans to call up another spinner at this stage, though Mitchell Swepson, the leg-spinner, is currently playing for Glamorgan.
Australia suffered a similar setback in 2005 when Glenn McGrath hurt his ankle. He stepped on the ball in the warm-up to the second Test at Edgbaston. He returned at Old Trafford with match figures of 5 for 201, before returning 5 for 157 at The Oval, but wasn't his usual force.
Steve Waugh defied a calf injury in 2001. He hurt himself at Trent Bridge, and even had to use a wheelchair. He missed the defeat at Headingley. His wife Lynette helped persuade him to play. "You are the captain, they need you," she said.
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