The timing of the replacement news is interesting and it seems like WWE found out sometime during Raw because he was still listed on the graphic as one of the participants but Tom Phillips mentioned that Mysterio would be in the match and there was no mention of Rusev. At the time of the show, Rusev was still listed for the show in the WWE.com preview.
Dave Meltzer provided an update on this story on Wrestling Observer Radio and the reason why Rusev is not going to Saudi Arabia is because he is injured. That is what he told WWE.
“The story is an injury. He backed out of the show, essentially,” Meltzer said.
Rusev has been in a contract dispute and there have been all sorts of rumors suggesting that he’s been unhappy with the company so the injury story is interesting.