DeGrom was scratched from his scheduled start Tuesday against the Cardinals due to side tightness, Jon Heyman of MLB Network reports.
The Mets insisted that deGrom was fine when they pushed his start back from Monday to Tuesday, indicating that they simply wanted to give him an extra day to rest. It now looks as though the decision may have been injury-related, though it's possible the side issue didn't show up until Tuesday. Per Jeff Passan of ESPN.com, deGrom is only expected to miss one start. Miguel Castro will be the team's first pitcher in what looks like a bullpen game Tuesday.