The situation: With right-handed starter Graham Godfrey struggling to miss bats in the big leagues, the A's reached into their suddenly deep minor league system to grab Parker, the top prospect received from the Arizona Diamondbacks for Trevor Cahill. He will make his Oakland debut Wednesday.

Background: Parker was the ninth overall pick in the 2007 draft, but there were pre-draft rumors that he could go as high as No. 3 overall to the Cubs. He was the first high school pitcher selected that June.

What he can do: He lived up to expectations early in his career, reaching Double-A in his second full season while generally being considered one of the top right-handed pitching prospects in the game. However, he developed elbow soreness late in 2009 and eventually underwent Tommy John surgery. After missing the entire 2010 campaign while recovering, he made a successful return in 2011, putting up a 3.79 ERA in 26 starts for Double-A Mobile while striking out 7.7 batters per nine innings. He topped it off by pitching 5 2/3 shutout innings in his major league debut against the Dodgers last September. The 23-year-old has a 2.14 ERA in 20 2/3 innings for Triple-A Sacramento, with 22 hits allowed, six walks, and 21 strikeouts.

Immediate big league future: Parker doesn't have the plus-plus power stuff from his pre-injury days, but it's still plenty good. Once touching 98 with his fastball, he now sits at 92-93 mph while occasionally touching 95, and the pitch features heavy sink and induces plenty of ground balls. His slider used to be an out pitch, but it's now the weakest of his offerings as a hybrid breaking ball that fluctuates between slider and curve breaks. Instead, Parker now gets strikeouts with a much-improved changeup that is now a plus offering that he'll throw at any point in the count. Like many Tommy John returnees, he has had some scuffles with his command and control — he has only a 61.2 strike percentage at Sacramento — and that's worth keeping an eye on Wednesday.

Long-term: Parker looks like he could be a No. 4 starter right now, but he's continuing to make strides in his return from surgery, and often big leaps are not made until the second year back. To some scouts, he still has the potential to be a No. 2 starter, and most see him as at least a No. 3.

A version of this story originally appeared on ESPN Insider Insider.

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Thanks for the information Kevin. How common is it for a pitcher to go through surgery (TJ or otherwise) and have some pitches 'no longer work' when they did in the past or vice versa as with Parker?
It's quite common.