New Blues boss Lee Clark admitted on Wednesday that negotiations are "ongoing" with Albion regarding Foster. Cologne keeper Michael Rensing is also believed to be on the list of possible contenders being targeted by the Baggies.
However, Foster remains their number one choice after his outstanding form when on loan from Birmingham last season.
He played a major role in West Brom finishing in the top 10 of the Barclays Premier League and was voted the club's player of the year.
Foster was linked strongly with a move to QPR before they signed Robert Green from West Ham, but the former Manchester United keeper has often made it clear he would be happy to remain at the Hawthorns.
Rensing will only come into the equation if attempts to sign Foster fall through.
Albion are also looking to sign a new left-back after the departure of Nicky Shorey at the end of last season.
But any hopes of bringing in Danny Rose on loan from Tottenham will have to be put on ice until the London club have resolved their managerial situation.
Midfielder Keith Andrews, who signed a short term contract with Albion after leaving Blackburn in January, is expected to move to Bolton.