Walker was removed from Tuesday's start against Atlanta after the second inning due to an apparent injury, Anthony DiComo of MLB.com reports.
New York lost Carlos Carrasco to an oblique strain Monday, and Walker has now been forced to exit after two scoreless frames a day later. The reason for Walker's removal remains unclear, but it's almost certainly an injury given he was pitching well and since the Mets are already coming off an impromptu bullpen game.