A corresponding roster move will be required to activate Marquis.
Marquis, who had bone chips in his elbow, made two rehab starts for Triple-A Syracuse, most recently allowing two runs on three hits over six innings on Monday. The veteran is signed for $7.5 million in 2011.
"He wants to contribute," Nats manager Jim Riggleman said. "If he's the real Jason Marquis, the guy who is sinking the ball and getting ground balls and attacking hitters, he can really help us and be a part of our future."
Riggleman added that lefty Scott Olsen, who was slated to start Sunday, remains in the club's rotation plans. Olsen would pitch as early as Wednesday. Stephen Strasburg, also coming off the 15-day DL, will pitch Tuesday.