SAN DIEGO – The Dodgers are going back to a six-man rotation again and the sixth starter isn’t even on the roster right now.

Veteran right-hander Dan Haren will not make his scheduled start on Wednesday against the Washington Nationals. Instead, the Dodgers will push him back to Friday against the Arizona Diamondbacks after an off day Thursday.

Rookie right-hander Carlos Frias is expected to take Haren’s spot on Wednesday. Frias was optioned to Triple-A Albuquerque in order to clear a roster spot for left-hander Hyun-Jin Ryu to come off the DL and pitch Sunday.

Major-league rosters expand on Monday and Frias can (and will) be recalled as soon as the minor-league season ends. The final Pacific Coast League games are Monday.

Dodgers manager Don Mattingly said there are no physical issues forcing the move with Haren. But Wednesday’s game is a 12:10 p.m. start at Dodger Stadium and Haren just pitched Friday night.

“With Dan, we looked at that as short rest,” Mattingly said of the early start. “We know we have games the 3rd and the 10th that are a little trouble so we’re going to give Dan the extra day.”

Nonetheless, Haren pitched a day game against the Milwaukee Brewers on four days’ rest two weeks ago — albeit poorly. He lasted just three innings, giving up six runs on five hits.

The real motive might be a little farther down the road. By moving Haren back to Friday and starting him in the Sept. 10 game Mattingly referred to, the Dodgers will be able to line up the front three in their rotation for both of their three-game series against the second-place San Francisco Giants in September.

After making his next start against the Diamondbacks next Saturday on extra rest for the third consecutive start, Zack Greinke would pitch the first game in San Francisco on Sept. 12 — also with an extra day’s rest. Ryu would pitch the second game on five days’ rest. Clayton Kershaw could then move ahead of Roberto Hernandez and pitch the series finale at AT&T Park on regular rest.

If the rotation holds after that, the same trio would be on regular rest for the three-game series against the Giants at Dodger Stadium on Sept. 22-24.

And if this is just a one-time shuffle, Haren is on track to get five starts in September. He needs just 24 innings to reach 180 for the season and activate a player option in his contract that would guarantee him $10 million for the 2015 season — if he plays in 2015. Haren (who will turn 34 in September) said he remains “undecided at this point” on whether he will play next season, option or no option.

“I know it’s there,” Haren said of the clause in his contract. “When I’m on the mound, I’m not thinking about any of that stuff. It’s more between starts and when people ask me about it that I have to think about it.”

Haren has averaged 52/3 innings in his 27 starts this season and the Dodgers could easily stop him short of the 180 innings needed to activate the option by skipping him in the rotation again — perhaps starting a young pitcher like Frias in his place if the Dodgers clinch a playoff spot. Haren wouldn’t say how disappointed — or angry — he might be if that happened.

“It’s hard to say,” Haren said. “I’d like to get there but not because of the contract. If I get there, it means I’m pitching good. If I don’t get there, I probably stunk.”

NOTES

Both Ryu and third baseman Juan Uribe were activated from the DL and started Sunday. … In order to clear roster spots for both, the Dodgers optioned infielder Miguel Rojas and Frias to Triple-A Albuquerque — for one day. Both can and will be recalled after the PCL season ends. The Isotopes have one more game Monday. But Mattingly said he expects the first wave of September call-ups to join the Dodgers in Los Angeles on Monday.

Contact the writer: bplunkett@ocregister.com