Manager Roy Keane admits striker Kenwyne Jones was a big miss for Sunderland against Portsmouth yesterday.
Keane says the extent of the Trinidad and Tobago international's injury is not fully known.
"He literally slipped in the last three minutes of training and we decided we were not going to take any risks," said Keane last night. "How serious we will know in the next 24 hours and that was obviously a big loss to us."
Without Jones, Sunderland lost an early lead as Portsmoth ralled to win. Jermain Defoe handed Tony Adams his first win as Portsmouth boss as Pompey came from behind to win.
The England striker converted an injury-time penalty after Black Cats substitute El-Hadji Diouf had tripped Glen Johnson.
Algerian midfielder Nadir Belhadj had earlier cancelled out Djibril Cisse's fourth-minute opener six minutes after the break, but the home side wasted a series of opportunities to kill the game off.