Sheamus, current WWE US Champion, wrestled in the Battle Royal on the WWE Battleground PPV on Sunday. However, he then was not on Raw this week, and despite being advertised for the main event of Smackdown, was not on the Smackdown Tapings.
Apparently Sheamus came down with a severe case of the flu, and missed Monday and Tuesday due to illness.
Because of WWE culture, it is usually frowned upon to miss TV tapings due to illness, so the assumption is that the flu is bad to the point where Sheamus could not possibly appear on TV.
This impacts the plans for the US Title for Summerslam, including chanages to the changes from last week.