SAN DIEGO -- Nationals right-fielder Jayson Werth, on the disabled list because of a right hamstring injury, was not involved in any rehab assignments the last two days because he felt tightness in the injured hamstring.

Werth was hoping to re-join the team Saturday, but the Nationals want Werth to get more at-bats before he is activated from the DL. It's not known when Werth will rejoin the team.

In an e-mail to MLB.com, Werth said he did not have a setback with the hamstring.

"No setbacks, but [I] did realize I wasn't quite ready," Werth said. "As I'm learning, hammys are tricky, as we have seen with Wilson [Ramos]. You gotta be 100 percent before coming off the DL. There are injuries you can play with/through and there are injuries you can't.

"Unfortunately, I don't think hammy injuries are the ones you can. [I'm] working hard and staying sharp. [I] just gotta be sure I'm ready to go when I come off the DL. Got a long hard road ahead and need to be healthy to contribute fully to the cause."

Detwiler to miss next start due to back injury

WSH@LAD: Detwiler leaves the game with ankle injury

SAN DIEGO -- Nationals left-hander Ross Detwiler will not make his next start Monday against the Giants due to a lower back injury, according to manager Davey Johnson.

"It sucks, but I totally understand it," Detwiler said. "It's early in the season and I don't want to re-aggravate it later. It's tough -- we have to take it kind of slow. All I can do is what they ever tell me to do."

Detwiler had a second MRI on Friday and the results were still inconclusive. He is getting more tests done Saturday. Johnson said Detwiler could have an oblique strain. The doctors are also going to check to see if there are any problems in Detwiler's vertebrae.

"He did say he felt a lot better," Johnson said."It doesn't hurt him when he sneezes or walks, so that is a good sign. He says he hopes he misses one start."

Detwiler sustained tightness in his lower back Wednesday against the Dodgers in the top the third inning on a sacrifice bunt that advanced Roger Bernadina to second base. Detwiler had problems running the bases. His back got worse in the bottom of the inning.

It was believed that he hurt his back while catching a wide throw from shortstop Ian Desmond in the bottom of the third, but Detwiler said he felt fine.

Detwiler had problems throwing pitches after that, and pitching coach Steve McCatty, head athletic trainer Lee Kuntz and Johnson came to his aid. Detwiler stayed in and allowed a single to A.J. Ellis and walked Andre Ethier to load the bases. He got out of the inning when Scott Van Slyke lined out to third baseman Ryan Zimmerman. The left-hander was then replaced by Craig Stammen.

"I feel all right, better than yesterday [Thursday] for sure. It's one of those things you have to take day by day," Detwiler said. "We'll see how I feel tomorrow, then next day and the next day."

With Detwiler missing his next start, Johnson must decide who will take the turn in the rotation. If Detwiler doesn't go on the disabled list, relievers Stammen or Zach Duke will make the start. Both players said they are ready to go if needed. One of them will be told by Saturday if they will make the spot start.

Stammen, who began his career as a starter, has a respectable 2.25 ERA in 11 games out of the bullpen this season. As a starter, Stammen is 8-11 with a 5.08 ERA.

"If I ever get to start again, I would be interested to see what I could do," Stammen said. "I feel I can do better. I'm older, more experienced. I feel like my stuff is better. I feel like I'm better than I was then. I'm more equipped to start."

Duke spent most of his career as a starter with the Pirates. If he gets the nod, he would have to get into a routine in order to be ready for Monday.

"You can tailor your program a little more. That's something I'm used to," Duke said. "At this point, we would probably be on a short leash. The main thing is, make sure that we are fresh on that day."

Johnson said that if Detwiler has to go on the disabled list, the Nationals will most likely call up a pitcher from Triple-A Syracuse.

Right-hander Chris Young and Ross Ohlendorf are candidates to be called up. Both players are off to slow starts as Ohlendorf is sporting a 4.96 ERA and Young has a hefty 7.96 ERA in five starts.

Strasburg happy to have family in stands

WSH@SD: Strasburg discusses performance vs. Padres

SAN DIEGO -- There were 50 members of Stephen Strasburg's family who watched him pitch a career-high eight innings and allow two runs -- one earned -- on three hits in a 6-2 victory over the Padres.

Strasburg hasn't seen his family in four months and was pleased they were able to see his first Major League game at Petco Park. Strasburg has pitched a handful of games at Petco Park in college as a member of the San Diego State Aztecs.

"It has been a long time. They are all working, so it's not like they could fly out and visit [me] much," Strasburg said. "It's amazing how all the little ones have grown so much. That's the nature of it. It's always good to catch up."

In the game against the Padres, Strasburg said he didn't change anything except trying not to do too much on the mound. The biggest improvement was commanding his pitches while pitching from the stretch.

"I'd say the biggest thing I try not to do is try too hard, trying to throw the perfect pitch," Strasburg said. "Take what it gives you and just go out there and not really get off of what I'm doing the whole game when a guy gets in scoring position. It seemed to work a little bit more last night.

"At the same time, there are going to be other games in the future where you are going to go out there and something happens. It appears you get discombobulated," he said. "But I think the bigger thing is, I'm getting more and more comfortable out of the stretch. Early on, it seemed pretty tough to command the fastball and command the off-speed [pitches] down the stretch. It's a work in progress."