However, the manager offered a positive update on the Sweden international, following the setback of losing Lucas Bergvall and James Maddison.
"Medical team are not too concerned with him, more of a knock than anything else, so we're hoping he should be OK," Postecoglou told the media.
"It's not helpful when you lose another player, it's the fine line we're trying to navigate at the moment. That aside, it was a disappointing performance and nowhere near the level it should be.
"Guys had an opportunity today to put their name forward and put some pressure on the guys who played the other night. Fair to say there wasn't any compelling evidence of that.
"That's what I'm trying to push with these guys, that sometimes in football you've just got to take the opportunities there before you. They're never going to be perfect.
"We made eight changes but there is an opportunity there and you've just got to take it when presented to you and I'm disappointed more didn't step forward today."