Matt Harrison started a rehab assignment yesterday, pitching 5 innings for the Round Rock Express in Reno, giving up 2 runs on 5 hits, a walk and 4 strikeouts. He had 49 strikes in 78 pitches.
The velocity reports had him in the mid-80s, and Harrison said afterwards that he needed to do some work strengthening his legs to improve that going forward. He also reportedly had some command issues with his fastball. But the important thing was that he pitched, had success, and hopefully, today, he'll feel good physically.
Harrison can spend up to 30 days on a rehab assignment, and my guess is that the Rangers will use all 30 of those days, especially if Harrison continues to have issues with his command. What happens after that will likely be dictated, at least in part, by what the situation is with the major league pitching staff, and any potential needs in the rotation.