Baggies manager Steve Clarke confirmed that Foster would not be rushed back into the first team having had a minor procedure in hospital last week.
Boaz Myhill deputised for Foster in last weekend's 2-1 victory at Wigan, and the Wales international will retain his place when the European champions visit the Hawthorns on Saturday.
Clarke hopes former England No.1 Foster will be fit in time for next week's trip to Sunderland, and he also revealed that "one or two players" had picked up knocks while on international duty and are doubtful to face Chelsea.
But midfielder Youssouf Mulumbu is confident he will be ready to take on former boss Roberto Di Matteo after suffering a hamstring problem against Wigan.
"I hope I will be fit," said Mulumbu, who pulled out of the Democratic Republic of Congo's friendly with Burkina Faso in Morocco.
"After Wigan I felt something in my hamstring and we didn't want to take any risks with me going to the international and coming back tired or with an injury.
"It happened during the Wigan game but the gaffer had made all of his changes so I had to stay on."
And on the prospect of taking on Di Matteo, he added: "Robbie has done very well. He is still quite young but he drove the Chelsea team on. So all my praise goes to him, but I'm looking to beat him.
"I won't be looking to shake any hands or be kind to people, I will be looking to get three points and maybe go fourth in the league. He has a strong team but let's see what happens on Saturday. I'm quite confident."