Neither had a significant setback, Brewers assistant GM Gord Ash stressed on Friday, but they were not progressing, either.
Henderson, removed from closer's role before Opening Day because of concern about his diminished velocity, has been on the disabled list since May 2, and twice went on Minor League rehabilitation assignments that did not produce the results all parties concerned needed to see. He visited Raasch in Milwaukee on Wednesday and underwent another MRI exam.
"His Minor League rehabs were successful because he knew how to pitch," Ash said. "But he wasn't feeling 100 percent and he finally admitted that, even though he wanted to be optimistic. He would pitch well one day, but he couldn't come back. That's when he said, 'I've got to get this looked at again.'"
Henderson will turn 32 in October and has one more pre-arbitration season remaining.
With Henderson struggling, Thornburg emerged as a bright spot for the Brewers, posting a 0.61 ERA and a .122 opponents' average through the end of April. But he had a 6.00 ERA and a .319 opponents' average in May and was placed on the disabled list during the first week of June with wrist-flexor irritation in his elbow. He never progressed to the point of a rehab assignment.
The Brewers have also been monitoring Thornburg's ulnar collateral ligament -- the tissue, if torn, that sends a pitcher for Tommy John surgery and a year-long rehabilitation. Thornburg's UCL is not torn, Ash said, but scans have detected what he termed "weakness."
"The follow-up MRI and second opinion he had 10 days or so ago showed there had been healing. Progress," Ash said. "So, nothing to be alarmed about. But he just can't get over the hump."
The PRP injection is intended to help. The Orioles' Chris Davis and Matt Wieters and Reds' Joey Votto are among the Major League players to undergo the procedure this season, in which a players' blood is drawn and placed in a centrifuge, after which activated platelets are injected into the injured area to speed healing.
Thornburg will resume activities in late September or early October. He turns 26 Sept. 29.
Adam McCalvy is a reporter for MLB.com. Read his blog, Brew Beat, and follow him on Twitter at @AdamMcCalvy. This story was not subject to the approval of Major League Baseball or its clubs.