Tottenham fear Jonathan Woodgate might have suffered a recurrence of the back injury that has blighted him for much of his career.
The former Real Madrid and Newcastle defender lasted just 10 minutes of Spurs' goalless draw with Manchester United on Saturday before being forced out of the action.
The 28-year-old was rushed straight to hospital after leaving the field at White Hart Lane following an innocuous challenge with Carlos Tevez.
Doctors attempted to establish the nature of Woodgate's new injury although Harry Redknapp's No.2 Kevin Bond has admitted they are at a loose end.
"He was in hospital with a back spasm but they're not sure of the prognosis," assistant manager Bond told The Sun.
Woodgate is almost certain to miss Thursday's home Uefa Cup clash against Spartak Moscow as it remains unclear how long he may need on the sidelines to recover.