Stoke City have confirmed that defender Robert Huth has suspected meningitis and is undergoing further tests in hospital.
Huth was taken to hospital on Monday after suffering from a virus which first became apparent during Stoke's recent trip to the United States.
The 27-year-old is due to have more tests on Wednesday and Potters boss Tony Pulis admits the situation is a 'massive worry'.
"It's a massive, massive worry for us, but the most important thing right now is Robert's health and we are keeping our fingers crossed that he'll be okay," Pulis told the club's official website.
"We don't know the full extent of it at the moment, but he'll be undergoing more tests, so hopefully we'll know more about the situation with him on Wednesday.
"He started to feel unwell just before we returned home from the United States last week and then felt a lot worse over the weekend."
Huth arrived in English football as a teenager with Chelsea in 2001, winning two Premier League titles with the Blues before moving to Middlesbrough in 2006.
After transferring to Stoke in summer 2009 in a deal initially worth £5million, he was named the club's player of the year and helped the Potters reach the FA Cup final in the 2010/2011 season.
Huth has played 19 times for his country and was part of the Germany squad which finished third at the 2006 World Cup on home soil.
Stoke begin their Premier League campaign at newly-promoted Reading on Saturday 18th August.