They also activated left-hander Jonny Venters from the DL and added right-hander Randall Delgado from Triple-A Gwinnett before Saturday's day-night doubleheader against Washington. Diaz batted .222 in 51 games. Out since July 5 with an impingement in his pitching elbow, Venters' lone rehab assignment came Friday for Gwinnett.
Delgado is scheduled to pitch the nightcap Saturday. He is 4-9 with a 4.52 ERA in 16 starts for Atlanta.
Lannan is also scheduled to start the second game of the doubleheader. He went 6-9 with a 4.89 ERA in 18 starts with Syracuse this season. He led the Nationals with 10 wins last season.