The Tottenham boss confirmed the Belgian defender had been injured in the second half incident in which he appeared to hurt his knee.
"He has an injury to his leg," said the Argentine. "It's difficult to assess now though, we need to wait."
Pochettino will be hoping that the defender, who was replaced by Eric Dier as Spurs chased a win at the Hawthorns, is not in too bad a shape with Spurs now facing three more away trips to Bayer Leverkusen, Bournemouth and Liverpool.
Cameron Carter-Vickers and Kevin Wimmer could be drafted into the manager's line-up for the match at the BayArena, although neither were even on the bench at West Brom.