It is common knowledge that Zack Wheeler missed all of the 2015 regular season because of Tommy John surgery. What may go under the radar, though, is that Wheeler also had two other elbow problems fixed during the surgical procedure: the repairing of a partially torn tendon and the removal of a calcium deposit. These are issues that Wheeler appeared to have been pitching through for some or possibly all of his professional career. Wheeler said that he has pitched with elbow pain throughout his entire career, even dating back to high school, and that the pain in his elbow became more dramatic in 2014. He was originally diagnosed with elbow tendinitis, but an offseason MRI after the 2014 season revealed the torn tendon and calcium deposits.
This conceivably could have had some sort of effect on his performance on the mound. In particular, Wheeler's command and control have both been problematic; control wise, his 10.2% walk rate and 53.6% first pitch strike percentage are both significantly below MLB average, and this is on top of a minor league walk rate of 10.6% in 74 starts. Of all MLB starting pitchers with at least 250 IP from 2013-present, Wheeler's walk rate ranks 5th highest, and his first pitch strike rate ranks second to last. I don't think it's farfetched to suspect a chronically barking elbow could contribute to command problems.
"We think coming off the surgery he's going to be pain-free and might be better than the guy we saw when he came up."
Wheeler, the former top 10 prospect in baseball according to multiple prospect outlets (BP, #5, MLB.com, #8), features an electric mix of pitches and a sky high ceiling. His fastball sits in the mid 90s and tops out at 99 mph, and he flashes a wipeout slider to go along with a power curve. On his best night, Wheeler's pure stuff is among the most elite in the sport. The excellent Jason Parks, formerly of BP and currently working as a scout for the Chicago Cubs, labeled Wheeler's future potential as a "1" starter in his winter 2012 "Prospects Will Break Your Heart" series over at Baseball Prospectus.
Simply writing about how nasty Wheeler's repertoire is doesn't do it enough justice, so here are some visuals of his peak stuff:
Fastball: 98 mph (73 pitches deep into the game)
Slider: 91 mph
Curve: 80 mph
Change up: 89 mph
Wheeler will likely be back in the Mets rotation in June or July, and will not be subject to an innings limit because of the midseason timing of his return.