The hamstring would make more sense as Victor has struggled with this injury since the beginning of the season, but with two reports suggesting there is something with his arm, maybe we are just now hearing about an injury that had been lingering and sapping Martinez of all of his power.
More updates to come...
Update - 8:26PM EST
MLB.com has now come out with its report saying that it is in fact inflammation of the elbow. According to the report,
"Martinez grounded out to short in his lone at-bat against Nick
Blackburn. He swung awkwardly and hit a slow roller to the left side of
the infield that shortstop Brendan Harris had to charge in on.
Martinez, unable to beat out the throw to first, was pulled and
replaced by backup Kelly Shoppach."
More updates when they arrive.