Decker has a partially torn rotator cuff and has missed the Jets' past two games.He will undergo season-ending surgery to repair the injury, a source told ESPN's Rich Cimini.
Decker was injured in Week 2 against the Buffalo Bills, but he played in every offensive snap the following Sunday against the Kansas City Chiefs. He caught only one pass in that game and later told team officials he had aggravated the injury.
Marshall's addition is an indication the Jets are concerned about the availability of cornerbacks Darrelle Revis (hamstring) and Darryl Roberts (shoulder) for Monday night's game against the Arizona Cardinals.
Decker has nine catches for 194 yards and two touchdowns this season.
ESPN's Adam Schefter and Field Yates contributed to this report.