The left-handed starter faced four teammates and simulated three innings on Sunday morning.
The Nats are hoping for good news, but the second opinion is usually a precursor to Tommy John surgery.
The Nationals placed Gio Gonzalez on the disabled list, adding to their lengthy list of injuries.
The outfielder hopes to return from his concussion on Saturday.
The third baseman will avoid the disabled list, at least for now, after an MRI exam on his shoulder revealed no structural damage.
In his first major league game in 20 days, the Nationals starter breezed through 3 2/3 innings and looked ready for the season.
Doug Fister felt encouraged after his bullpen session, but he was not prepared to look too far ahead.
The right-hander is scheduled to throw a Friday bullpen session, his first since his elbow discomfort first appeared.
Third baseman says he would play if it were the regular season.
The Nationals' starter, dealing with elbow inflammation, threw from flat ground on Wednesday and said he'd be ready to go when the games count.