West Brom need to stay a division above Birmingham City if they are to sign Ben Foster on a permanent deal at the end of the season.
Foster joined Albion on loan from the Blues during the summer transfer window with Boaz Myhill moving in the opposite direction.
And the agreement stated the 28-year-old will go back if Chris Hughton's Championship side are able to gain promotion to the Premier League.
"The deal with Birmingham is that if they get promoted there is no availability to buy, so if they go up Ben will definitely be going back," Albion's sporting and technical director Dan Ashworth said in The Birmingham Mail.
"When we did the deal in the summer we said it wouldn't be considered if they got promoted or we got relegated, so if we're in the same division next season then that will be the case.
"If we're not, we would need, and will take, a goalkeeper.
"Ben has come in and done really well and we would have to consider."
Birmingham are 13th in the Championship with three games in hand on their play-off rivals, but they will have to go on an ultra-consistent run to enter contention for automatic promotion.