From the Tampa Tribune:
Turns out we were slightly premature saying that he was called up on Friday, but not by much. The Rays will likely wait to make this move official until right before Tuesday's game, since it has the added benefit of giving them an extra available pitcher until then (Sonny or Gomes, depending who is demoted) and on delaying Cobb's service time by a few days.
The 23-year-old Cobb has made eight starts in Triple-A this season, and has carried over last year's success from Double-A. He's striking out over 9 batters per nine innings pitched and walking fewer than 2 batters per nine, posting a 1.14 ERA and 2.33 FIP. Odds are he won't carry over those numbers to the majors, but he doesn't have to in order to still be valuable: he just has to be better than Andy Sonnanstine. And right now, that's a pretty easy bar to meet.
We'll have more on Cobb before his start on Tuesday, but get excited. Finally, the Rays will be throwing their best option out there in Niemann's spot.
EDIT: Now this addition from Rick Stroud at the St. Pete Times:
Apparently, the Rays plan a return to the bullpen for RHP Andy Sonnanstine, who became the fifth starter when Jeff Niemann went on the disabled list May 6 with a lower back strain. Sonnanstine is 0-1 with a 4.21 and the Rays lost all three games he started in place of Niemann, who still is at least several weeks from re-joining the team.
I'm not sure if that's just speculation or inside info, but it sounds like that's coming from someone on the Rays. And if that's the case, Brandon Gomes is likely heading back down to Durham. Darn.