"Ball was coming out good, legs were underneath me and I feel ready," he said.
Papelbon, who is recovering from a right intercostal strain, said he would likely throw a simulated game on Wednesday.
"I don't see why I shouldn't be ready to go after that," Papelbon said.
But the Nationals are normally cautious with players coming back from injury and might not want to rush Papelbon back. Earlier in the day Monday, manager Dusty Baker said Papelbon's sharpness will be a factor.
"He'll probably want to come back sooner rather than later, but I would choose to have him come back when all of us feel he's ready sharpness-wise," Baker said. "It's been killing him to be sitting in the dugout while we're losing, but we have to put that aside and think about what's best for him and what's best for us in the long run."
Jamal Collier covers the Nationals for MLB.com. Follow him on Twitter at @jamalcollier. This story was not subject to the approval of Major League Baseball or its clubs.