SAN FRANCISCO — Just as they hoped to gain momentum for a last-ditch playoff run, the Mets absorbed another hit to their vaunted starting rotation when Steven Matz was placed on the disabled list Monday with a shoulder injury.
Though an MRI exam revealed no structural damage, the Long Island native was diagnosed with what the team called “left shoulder tightness.” The move is retroactive to Aug. 15.
Righthander Robert Gsellman was promoted from Triple-A Las Vegas to take Matz’s spot on the roster. He will pitch in long relief, with righthander Seth Lugo set to take Matz’s spot in the rotation. He will pitch on Thursday against the Cardinals.
Gsellman, 23, is one of the Mets’ top remaining pitching prospects. He went 1-5 with a 5.73 ERA in nine starts with Triple-A Las Vegas in the hitter-friendly Pacific Coast League after beginning the season with Double-A Binghamton and compiling a 3-4 record and 2.71 ERA in 11 starts.
In addition, second baseman Neil Walker officially will be placed on paternity leave before Tuesday night’s series opener against the Cardinals. To take his place, the Mets will recall infielder T.J. Rivera from Las Vegas. Rivera, 27, hit .355 (11-for-31) during his first stint with the Mets earlier this month.
The absences only complicate the challenge facing the Mets (62-62), who are 4 1⁄2 games behind the Cardinals for the final wild-card spot.
Matz, 25, is 9-8 with a 3.40 ERA in 22 starts. The lefthander had remained in the rotation despite a painful bone spur in his elbow that was revealed in June. Now he will be shelved with the Mets fighting to keep their slim chances alive.
The Mets’ brilliant rotation already had taken a major hit, losing Matt Harvey to surgery to correct thoracic outlet syndrome. That occurred after he muddled through the worst season of his career.
Jacob deGrom endured a dip in velocity earlier in the season before bouncing back. Noah Syndergaard also is pitching through a bone spur, though his is not as severe as Matz’s.
With both, the Mets intend to be mindful of their workloads, part of the reason manager Terry Collins opted to remain in a five-man rotation despite Monday’s off day.
That choice means lefthander Jonathon Niese will keep pitching on turn, though his struggles as a starter with the Pirates is the reason he was traded back to the Mets.
Later in the week, the unheralded Lugo will make only his second big-league start.