The Nationals optioned Adon to Triple-A Rochester on Wednesday.
Adon's demotion comes after he took his league-high 10th loss of the season while giving up eight earned runs in three innings during Tuesday's 12-2 loss to the Marlins. The rough outing inflated Adon's season ERA and WHIP to 6.95 and 1.76, respectively. With Adon heading to the minors, Evan Lee is expected to take over as Washington's No. 5 starter.