"It just wasn't as comfortable as I wish it would have been," Venters said. "We'll see what tomorrow brings and we'll go from there."
When Venters was able to throw off flat ground without any discomfort over the past week, he knew his first test would come when he put some added stress on his elbow by throwing on a downward plane off a mound.
"It was just a different stress than you put on it when you throw off flat ground," Venters said. "It might be one of those things where it's got to get used to throwing off a mound again. It didn't feel great. But we'll see how it feels tomorrow."
Venters battled elbow discomfort during the final two weeks of Spring Training and received the PRP injection after being evaluated by Dr. James Andrews. MRI exams were inconclusive because Venters had already undergone Tommy John elbow ligament reconstruction surgery. Andrews performed the procedure in 2005.
Venters rested his arm for four weeks after receiving the injection, which is intended to stimulate the healing of bone and soft tissue. He is hoping his latest setback was simply a product of normal soreness. But it did not seem to be a good sign when he confirmed he felt discomfort immediately after starting Thursday's mound session.
"I was putting something on it for sure," Venters said. "The ball was coming out decent. It just didn't feel very good."
Venters was one of the game's top relievers while posting a 1.89 ERA and combining to make a Major League-high 164 appearances during the 2010 and '11 seasons. He battled elbow discomfort last year and spent two weeks on the disabled list in July.
Mark Bowman is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.