"We're still in wait-and-see mode," Silverman said. "And expect to have an update the next couple of days when we get back to St. Petersburg.
"Obviously any time there is a setback, it's concerning. Alex is a competitor. He's going to do everything he can to fight through this. And we'll have a lot more clarity in the coming days and the coming weeks."
Cobb had been throwing off a mound since April 24 after experiencing right forearm tendinitis during Spring Training. But he did not throw off "flat ground" Sunday as expected.
"He's had some tests performed and we're awaiting results," Silverman said. "He was throwing. He was progressing, but then had a setback. That was the reason for the medical investigation."
Silverman said that the Rays were not aware of Cobb furthering his injury during the rehab process.
"We have followed and continue to follow normal protocol with this type of injury," Silverman said. "It was a forearm strain. The forearm is closely connected to the elbow, so there's always concern with forearm strain.
"Alex was progressing well with his rehab until this last setback. And so now we're back in the evaluation mode. ... Just a setback that makes us all pause to try and figure out what the cause is and how we go forward. He was comfortable."
Cobb has seen team orthopedic physician Koco Eaton, and Silverman acknowledged there is a possibility that he will be examined by Dr. James Andrews, who is well known for performing Tommy John surgeries.
"Once we go through those tests and work with the doctors we'll have more to update you on," Silverman said. " ... Right now, we're focused on him getting back into a routine. And restarting the rehab. I know that's Alex's focus and that's ours, too. ... We're taking a deliberate approach with him and making sure that we know exactly what he's dealing with before we take any next steps."
There's speculation that Cobb could try to pitch through the injury since it's a partial tear.
Cobb initially began to feel the effects of his injury during a March 17 Spring Training game against the Phillies in Clearwater, Fla. He went to Spring Training slated to be the team's Opening Day starter.
Cobb was one of four Rays starters to begin the season on the disabled list, along with Drew Smyly (left-shoulder tendinitis), Alex Colome (pneumonia) and Matt Moore (Tommy John surgery).
Smyly and Colome are back in the rotation and Moore appears likely to be back before Cobb, which Silverman acknowledged.
"Yeah, there's a possibility," Silverman said. "We don't have a timetable on Alex at this point. Matt Moore is on the schedule that we laid out for him many months ago and he's progressing well.
"We've been looking to get both of those guys back and hopefully we get both of them back as soon as possible. Matt Moore is on a defined timetable and it's looking like it's going to be June-ish for Matt Moore. Once we know what Alex is dealing with, will have a better sense about his timetable."