Peterson will start Sunday against Arizona, Tim Healey of Newsday reports.
The lefty is the seventh starter on the Mets' depth chart and didn't even make the Opening Day roster, but he'll be needed already in the 10th game of the season after Jacob deGrom and Taijuan Walker were sidelined with shoulder injuries. Peterson pitched four innings of scoreless relief after Walker exited his start Monday against the Phillies, so he's stretched out and on schedule for Sunday's outing. Through 24 career major-league starts and two relief appearances, Peterson owns a 4.49 ERA and 1.31 WHIP. He could get the chance to make multiple starts in place of Walker, who's expected to require a rehab outing.