The duo suffered hamstring and knee problems respectively during Sunday's draw with Midlands rivals Aston Villa.
"We gave quite a positive injury bulletin midweek but unfortunately this game has come too quickly for some people," said Clarke.
"[Boaz] Myhill, [Steven] Reid, Jones and Brunt won't be fit. We are missing a few bodies.
"Hopefully it won't affect us at all because we've shown this year that we have a good squad. We've utilised the squad well."
The sixth-placed Baggies go into Saturday's match at The Hawthorns with three wins from their opening six matches.