Hanson will first make a rehab start for Single-A affiliate Inland Empire, which will go for roughly four innings or 60-70 pitches. If the start goes well, he will be able to return to the Angels on a limited pitch count.
The team currently only has four starters, with Jason Vargas still on the disabled list with a blood clot. They do not have much pitching depth at this point, depending on Joe Blanton despite his 5.53 ERA for the season.
Hanson has a long history of arm injuries, so it would potentially be beneficial for the Angels to be careful and make sure he's fully healthy before setting him loose. For a team mostly out of contention, it would be reckless to risk future seasons by rushing Hanson back.