Walker was placed on the 10-day injured list with right shoulder bursitis Tuesday, Anthony DiComo of MLB.com reports.
Walker himself wrote on Twitter that, "everything is all good" Tuesday after leaving his start Monday against the Phillies with right shoulder irritation, but "all good" was apparently in relation to avoiding a more severe injury. He'll still wind up missing at least one start and potentially a small handful, with the Mets yet to specify exactly when he'll be back. David Peterson pitched four scoreless innings of relief after Walker's exit Monday and is presumably in line to fill his spot in the rotation.