Blackburn (forearm) threw four innings during his start at extended spring training Friday, Jane Lee of MLB.com reports.
Blackburn came out of the outing with no further setbacks in his recovery from the forearm strain, so he'll kick off a rehab assignment with High-A Stockton later this week. The right-hander is expected to work up to 60 pitches in his first rehab outing and will likely require at least 2-to-3 starts in the minors beyond that before the Athletics entertain activating him from the 60-day disabled list.