Rodriguez, who experienced tightness in his left forearm while doing some flat-ground throwing on Friday, has been shut down and has an appointment with the team's medical staff. It is the same condition that forced him out of a June 5 start in Atlanta and onto the DL.
McDonald will see Dr. Keith Meister in Dallas on Tuesday for confirmation of diagnosis of the source of his shoulder discomfort by team doctors. McDonald declined to disclose that diagnosis, characterizing it as premature.
If Dr. Meister's findings differ, McDonald plans to seek a third opinion from Dr. James Andrews. Otherwise, he will turn his attention to curing the condition that has ailed him all year.
"I'm eager to find out just what's going on," said McDonald, who conceded that he hasn't felt right, even while he was part of the Pirates' regular rotation through April. "At the beginning, there really was no pain, it just felt different. Then when it started to hurt, I thought, 'There's something wrong. We've got to look at this.'"
McDonald was on a conservative throwing program until starting a Minor League rehab assignment on May 27.
"After not throwing for a while, my first couple times out, I felt fine," McDonald said. "Then the same pattern started over again, where I couldn't get loose and had the discomfort."
McDonald made the last of his six rehab starts on June 22.
On the positive side, Burnett had a problem-free 38-pitch bullpen session on Friday. On Tuesday, he will throw a simulated game spiced with elements of his biggest challenge, the ability to charge off the mound to field the position.
Tom Singer is a reporter for MLB.com and writes an MLBlog Change for a Nickel. He can also be found on Twitter @Tom_Singer. This story was not subject to the approval of Major League Baseball or its clubs.