Partial Source: The Wrestling Observer
Mark Henry is still out after a minor shoulder injury he suffered at Extreme Rules. As noted, it's not all that serious and he asked for time off. As noted yesterday here on the website, there is currently major heat backstage on Mark Henry in WWE. WWE creative reportedly had a major storyline planned for him, but in the past week Henry contacted WWE and asked for time off to heal from nagging injuries including the minor shoulder injury.
While WWE tells their performers they want them to rest when they are hurt, the feeling right now is that WWE is upset with Henry. They did a lot to build Henry up and get him hot again, only for him to ask for time off right after.