Morse re-aggravated the right lat muscle he first strained March 6 on Monday night during a rehab appearance with Class A Hagerstown. The Nationals had expected Morse to make his season debut today in their home opener. Instead, they are left to wait on a hitter who crunched 31 home runs and hit .303 last year before a two-year, $10 million contract extension.

“We tried to ramp him up, get him ready as quickly as we could, because he’s a big piece of our lineup,” Rizzo said. “He just re-aggravated it. So now we’re going to have to be ultra cautious to make sure that he’s right for the majority of the season.”

The Nationals have “no viable surgical option” for Morse, Rizzo said, and so Morse will only rest. The Nationals have not placed a timetable on how quickly Morse could prepare for the season following his six weeks on the sidelines. It seems a conservative estimate that Morse will miss the season’s first 50 games.

Without Morse, the Nationals have played Mark DeRosa and Xavier Nady in left field. They will soon add center fielder Rick Ankiel, who has spent the season’s first week on the disabled list with tightness in his left quadriceps, to their outfield mix. Ankiel will play for Class AAA Syracuse tonight and, if all goes well, will work out with the Nationals on Friday and return Saturday.

Rizzo said Morse’s injury will not affect top prospect Bryce Harper’s timetable to arrive in the major leagues, but Rizzo acknowledged Harper could eventually help fill the hole left by Morse.

The Nationals feel content about their internal options to replace Morse, but they will also consider outside choices. The Nationals scouted Diamondbacks outfield Gerrardo Parra during spring training, but the Diamondbacks were unwilling to move him for a price the Nationals deemed reasonable, and that trade seems unlikely.

“We’re comfortable with the people we have,” Rizzo said. “If there’s a viable option, if there’s a guy that fits what we’re trying to do this year and long term, we’re always open for that. We like the options that we have here. We’ve got a guy in Syracuse that’s an option for us. We feel good about where we’re at. … We’ve got in-house candidates that we feel comfortable with. It doesn’t change where we’re at with Bryce’s timeline at all.”

When Morse hurt his lat in the first day of spring training, the Nationals expected he would miss a few days, a week at most. He appeared in two games, March 12 and 13, as a designated hitter. But he never felt strong throwing the ball, and Monday night he re-aggravated the strain while making a throw in cold weather.

“It surprised us at the time,” Rizzo said. “We thought it was just a slight little pull. It’s been re-aggravated several times. I don’t know what caused it or what went wrong. We followed our protocol in trying to get him ready. He just hasn’t progressed.”

Manager Davey Johnson said the left field situation would be “a work in progress,” with playing time decided on how players perform. But he said he believed the Nationals had enough power in their lineup without Morse.

“I think if you look at the organization and the lineup, everybody in the lineup is capable of going longball,” Johnson said. “I don’t think that’s the critical factor in taking 30 bombs out of the four hole. Everybody is capable of elevating, not just hitting home runs, but getting better in every front, being a better hitter. If we settle in and do the things to have quality at-bats like every guy in this lineup should have, we’re fine.”