Newcastle midfielder Kieron Dyer is set to miss Saturday's game against Birmingham with a mystery illness.
Dyer played for the first time this season in the 3-0 win over West Brom on Sunday following a hamstring tear.
But Dyer, 26, has broken down again and has been referred to a specialist in an effort to clear up the problem.
A club statement read: "Kieron Dyer has a medical problem which has contributed to his lack of fitness. Unfortunately, he has suffered another reaction."
Michael Owen, Emre, Albert Luque and Titus Bramble have also had hamstring trouble this season, prompting the club to move training grounds.
Dyer has been repeatedly sidelined for long periods since his £6m move to Newcastle in 1999.
Before last Sunday's game, he had not played since the 2-0 home defeat by Manchester United on 28 August.