JONAS Olsson is facing an uphill battle to be fit for Saturday's Hawthorns date with Preston (ko 3pm).
The vice-captain was unable to return for the second half in the vital 2-0 win at promotion-rivals Swansea due to a calf problem.
The injury will be further assessed today - but Roberto Di Matteo is already resigned to losing the Swede's services against the Lilywhites.
And with Roman Bednar (thigh), Steven Reid (groin) and Jerome Thomas (hamstring) all missing last night, the head coach could not hide his concern at his mounting injury problems.
"Jonas has a little injury in his calf," said Di Matteo.
"That's why we had to make a change at half-time.
"He shouldn't be out for too long but it's one more on our injury list and he'll be very doubtful for our next game.
"I am a bit concerned about our injuries.
"We already had plenty and now that includes Jonas."
Olsson was replaced at half-time by Gianni Zuiverloon, who slotted in at right-back while the once-again impressive Gabriel Tamas moved across to deputise at centre-half for Olsson.
It was Zuiverloon's first action since his costly mistake in the FA Cup fifth-round exit against Reading six games ago.
And Di Matteo was pleased with how the former Dutch Under-21 international responded.
"Gianni did well in the second half," he said.
"It was a big test for him.
"Let's hope he keeps doing well."
