Alex Wakely, the Northamptonshire captain, has withdrawn from his side's County Championship match against Sussex and been replaced with a concussion substitute after suffering a head injury at home.

The 30-year-old Wakely was taken ill before play on the second morning, telling medical staff at the club that he had hit his head on a low beam at his home. An assessment on the ground detected signs of concussion and determined that he could take no further part.

Northamptonshire have been given permission to replace Wakely in the team with a concussion substitute, in this case Josh Cobb, who has been cleared to take Wakely's place as a batsman, although he will not be allowed to bowl.

David Ripley, the county's head coach, said: "Alex actually drove to the ground this morning as normal but was sick after he got here and it was clear he was not well.

"He explained that he had banged his head on a beam last night and after an examination by our medical staff it was decided he was showing signs of concussion. He has not gone to hospital but clearly we are monitoring his condition to see how he progresses. His welfare has to come first.

"We were not sure we would be allowed a substitute as the injury did not happen during the game but the regulations do allow it and after we had spoken to the Sussex captain it was agreed that Josh Cobb could take his place.