CINCINNATI -- When reliever Jared Burton first strained the latissimus muscle on his right side just before the All-Star break, he thought he'd be out just a few games.
On Friday, Burton missed his 27th game. He's been on the disabled list since July 19. Instead of working in a game, he threw a bullpen session at 70 percent intensity with the catcher positioned in front of the plate.
"I will hopefully test it out a little more on Sunday and see how it goes," Burton said.
There is no timetable yet for a return, partially because his rehab was slowed by a setback last week when he tried to pitch off a mound at full speed.
"It's like not even there as an everyday thing. When I work out, you don't even feel it," Burton said. "But the explosive arm speed of gearing it up and letting it go, that's when it gets me. It's been very frustrating. I can do anything else, but when I try to pitch and throw the way I throw ... I can't perform."
Burton's injury was especially unfortunate because he was having a strong second season for Cincinnati. In 43 appearances, he was 4-1 with a 2.23 ERA. He walked 17 and struck out 50.
On Thursday, Burton long tossed from a distance of 150 feet with no issue. Because he's felt good, Burton has been tempted to test his injury, but he also is apprehensive of the potential consequences.
"I'm optimistic as a person," Burton said, "but this has been very hard and frustrating to have it in the back of my mind, 'uh-oh, is it going to do it again when I get on the mound?'"
Mark Sheldon is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.