(Photo by Toni L. Sandys/The Washington Post)

(UPDATE, 4:35 p.m.) The Nationals announced their call-ups, and along with the four players listed below, relievers Aaron Barrett and Xavier Cedeno will join the team.

First baseman/outfielder Tyler Moore, right-hander Blake Treinen, outfielder Steven Souza Jr. and catcher Sandy Leon will be among the Nationals’ first September call-ups Monday night when they begin a three-game series against the Dodgers in Los Angeles, according to a person familiar with the situation.

All four Class AAA Syracuse players have played with the Nationals this season. Moore, a popular teammate in the Nationals’ clubhouse, will provide a backup first baseman and power off the bench. In 84 games at Syracuse, Moore hit .265/.367/.434 with 10 homers, 47 walks and 77 strikeouts.

Souza can hit for power and runs well enough to pinch run. He won the International League MVP award, hitting .350/.432/.590 with 18 homers, 52 walks and 26 steals.

Treinen will provide long relief and soak up innings in lopsided games. He made several spot starts in Washington this season, filling in when Gio Gonzalez hit the disabled list. At Syracuse, he posted a 3.35 ERA in 80 2/3 innings, striking 64 and walking 20.

Leon will provide a third catcher and has experience with the Nationals pitching staff. His presence will allow Matt Williams to pinch hit Wilson Ramos on days Jose Lobaton catches, which is a significant advantage. Leon hit .229/.321/.371 at Syracuse this season.