Strasburg was supposed to pitch Monday against Dodgers left-hander Clayton Kershaw, but was scratched because of an upper back strain.
Papelbon, who is on the disabled list because of a right intercostal strain, threw on flat ground Tuesday. He hopes to throw off the mound in Milwaukee.
After throwing in Milwaukee, Papelbon hopes to start a rehab assignment with Class A Advanced Potomac.
"It feels really good," Papelbon said before Wednesday's game against the Dodgers. "Right now, at this point, I just don't want any setbacks. I'm doing everything not to get any setbacks and continue to move forward in my progression and health. I'm excited and ready to get back out there."
Papelbon hurt his rib cage warming up before he entered the game against the Phillies on June 12 at Nationals Park. In that game, Papelbon allowed a solo homer to Maikel Franco in the ninth inning. Once Papelbon entered the dugout after that half-inning ended, Baker didn't like the way Papelbon was stretching his body. Papelbon ended up getting the victory, thanks to a game-winning hit by Jayson Werth.
The next day, Papelbon couldn't straighten out his body. So Baker ended up using Shawn Kelley in a save situation against the Cubs. Kelley picked up his first save of the season after striking out four batters in 1 2/3 innings.
Before going on the disabled list, Papelbon had 16 saves and a 3.28 ERA. However, baseball observers have noticed that his velocity is down to 91 mph. Papelbon said, however, that his job is to get outs.
"It's a big deal because of the sabermetrics stuff," he said. "You have radar guns in every city you go in. The big deal to me is getting guys out."
Bill Ladson has covered the Nationals/Expos for MLB.com since 2002 and writes an MLBlog, All Nats All the Time. He also can be found on Twitter @WashingNats. This story was not subject to the approval of Major League Baseball or its clubs.