The former England international was below full fitness for Monday night's home win over Southampton and was unable to kick with his preferred left foot.
Foster was ruled out of the final game of last season against Arsenal at the Hawthorns with a groin injury and also missed part of pre-season.
Albion hope today's [Thursday] prognosis will determine the extent of the injury and Baggies head coach Steve Clarke is still hopeful Foster may be fit for Saturday's Barclays Premier League game at Wigan.
Clarke said: "Ben is in Germany. Most of you noticed on Monday night that he was kicking with his right foot and not his left foot.
"He has gone out to see a specialist. We are waiting on the diagnosis. Fingers crossed, it is positive and I'm hopeful he is available to play again at the weekend, kicking with his right foot.
"It is a problem with the groin and hopefully it is something we can manage in the same way as with Shane Long and his hamstring over the last few weeks.
"If we can manage him, then we can get a few more games out of him. What are his chances for Saturday? Probably 60-40 in his favour."
Clarke admits he has no knowledge of whether Foster has been troubled in the past with his kicking.
He said: "Ben has never mentioned that he has got problems with his kicking to me.
"I know he likes to play from the back, he doesn't always like to kick the ball long but he has a good kick on him.
"We will deal with it and hopefully he is okay for the weekend and we can talk about football and not injuries."
If he is ruled out, then number two Boaz Myhill is set to deputise against the Latics.
But head coach Clarke has faith in Myhill who, if he faces the Latics, will be making his first Baggies appearance for 21 months since the opening game of the Roy Hodgson era.
He said: "We've got good back-up keepers here. Myhill played on loan in the Championship last season (at Birmingham) and had a really good season.
"He trains well every day and, if I have to rely on Boaz to play, I would be happy with that."