Source: The Wrestling Observer Newsletter
The Big Show has been working out down at the WWE Performance Center in Orlando, Florida. Show is doing so to rehab following a hip procedure, which is why he has not been back on TV.
We noted on Tuesday that The Big Show went in for a check-up last Friday and was still not cleared to return. Show had another check-up on Monday before RAW and was finally cleared to return. Despite that, the show had already been re-written numerous times throughout the day and they opted not to use him as it was simply too late. He'll be back very soon.
We'll keep you posted as we hear more.