Eoin Morgan has been ruled out of Middlesex's final County Championship fixture of the season against Worcestershire at New Road tomorrow after failing to recover sufficiently from the blow to the head he took while batting against Mitchell Starc in last week's fifth ODI against Australia.
Morgan, England's limited-overs captain, was forced to retire hurt on 1 during the seventh over of the series decider at Old Trafford on September 13, when he took his eyes off the ball from Starc that struck him a fierce blow on the side of the helmet.
After a lengthy period of treatment on the field Morgan was forced to retire hurt, and he did not return either to complete his innings as England were bowled out for 138, or lead the team in the field during Australia's series-sealing eight-wicket win.
Angus Fraser, the Middlesex director of cricket, confirmed that the club were following the current advice from the ECB medical team, which recommends that players who have shown signs of concussion need to be symptom-free for a full week prior to their next fixture.
Morgan, who was described by Trevor Bayliss, the England head coach, as "having a lump on his head and a headache" after reportedly taking an hour to come fully to his senses in the dressing room, was apparently still worse for wear last Tuesday morning, a full 48 hours after the incident.
"To be eligible to play in the next game after suffering concussion, the ECB advice is that a player has to show no symptoms for a week," Fraser told ESPNcricinfo. "Unfortunately Eoin was still a bit groggy and fuzzy when we assessed him last week. He is absolutely fine now and I'm sure he would be available to play if there was another fixture next week."
The management of head injuries in cricket came sharply into focus last November following the death of Phillip Hughes following a blow to the head during a Sheffield Shield fixture between South Australia and New South Wales at the Sydney Cricket Ground. That incident was clearly on the minds of several of the Australian players at Old Trafford, not least Starc, who had been fielding for NSW when Hughes was struck, and was visibly shaken by this latest incident as he was comforted by his coach, Darren Lehmann.
In common with many other sports, such as Australian Rules Football and America's NFL, the ECB this season introduced new guidelines for counties when dealing with concussed players, a move that has become imperative for all sports administrators following a study into Chronic Traumatic Encephalopathy (CTE), a progressive degenerative disease of the brain that was recently found to be present in 96% of a study of ex-NFL players.
This season has involved several high-profile head injuries, not least the on-field collision between the Surrey fielders Rory Burns and Moises Henriques at Arundel in June. Burns, who suffered cuts above his left eye as Henriques sustained a broken jaw, was back playing for Surrey within a fortnight.
An ECB spokesman confirmed that Middlesex took the decision to rest Morgan last week, having followed the current advice and guidelines from the ECB medical team.
This article was amended at 2130 on September 21, 2015 with additional information.
Andrew Miller is UK editor of ESPNcricinfo. He tweets @miller_cricket