Guerra (hamstring) returned to the Nationals as a non-roster invitee Monday, Jesse Dougherty of The Washington Post reports.
The 35-year-old threw 15.2 innings last season before his campaign was cut short by a hamstring strain. It's unclear whether or not the issue will carry over into spring training. Guerra owns a 3.73 ERA in 296.2 career innings of relief, though his 4.84 mark over the last three seasons is considerably less impressive.