Tonight's bullpen is going to be very short-handed if Mariano Rivera and David Robertson are both unavailable and Shawn Kelley is injured. In order to try and lengthen their depth, Matt Daley has been called up to the majors and Corban Joseph has been placed on the 60-day DL to clear a spot on the 40-man roster. The 31-year-old Daley signed with the Yankees before the 2012 season in his attempt to return from shoulder surgery. He finally got to pitch this season as he put up a 2.02 ERA and a 12.5 K/9 across three different levels in 53.1 innings, making the call up well deserved.
CoJo has been on the disabled list after undergoing season ending shoulder surgery months ago. He's taken up a spot on the roster all this time because to place a minor leaguer on the 60 you first have to technically call him up and, presumably, pay him like a major leaguer. The Yankees being unwilling to make this move earlier is what led to Melky Mesa being released by the organization.
Other players that could have been in line for the call up that are not on the 40-man roster are Chase Whitley, Chris Bootcheck, Sam Demel, Jim Miller, and Graham Stoneburner. The easier move to make could have been calling up someone like Jose Ramirez or Nik Turley, who are on the 40 and would not have required moving Joseph anywhere.