Stoke City defender Robert Huth has suspected meningitis.
The club are hoping to find out more about his condition in the next 24 hours.
The defender is due to undergo further tests to determine the strain of meningitis and the prognosis in terms of recovery.
Huth was rushed into hospital on Monday after the symptoms which became apparent in the US got progressively worse following his return home.
Boss Tony Pulis said: "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."
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