WASHINGTON -- Outfielder Roger Bernadina was scheduled to hit second and play right field for the Nationals on Saturday, but he was scratched because of lower back tightness. Willie Harris replaced him in the lineup.

Before the game, a team spokesman said that Bernadina was available to pinch-hit, but in the bottom of the fifth inning, manager Jim Riggleman had to use right-hander J.D. Martin as a pinch-hitter for Stephen Strasburg because Bernadina was in too much pain. Riggleman wanted to save his position players such as Mike Morse, Cristian Guzman and Alberto Gonzalez for the late innings.

With the day off Monday, Bernadina will not play until Tuesday against the Padres.

Although Bernadina was picked off to end the game Friday, Riggleman said he will continue to play Bernadina on a regular basis. Riggleman is thinking about leaving Bernadina near the top of the order. However, Riggleman would like Bernadina to hit sixth or seventh in order to drive in runs.

Riggleman opts for middle-infield rotation

WASHINGTON -- The Nationals find themselves in a rut, so manager Jim Riggleman went back to the drawing board and decided to go back to the rotation of players at middle infield, meaning Ian Desmond, Alberto Gonzalez, Cristian Guzman and Adam Kennedy will alternate between second base and shortstop.

The move means that Guzman will no longer be the everyday second baseman and Kennedy will play more at the same position than he had in the past month. Desmond will continue to see most of the time at short. Riggleman indicated he wants to see Desmond get 500 at-bats.

Kennedy started the season as the everyday second baseman, but lost his job in May when Guzman started swinging a hot bat. That month, Guzman hit a National League-best .381 with eight RBIs.

"There is some tinkering with the lineup," Riggleman said. "I think the one thing I would probably try to get back to is, get Kennedy more involved and get Gonzalez a little more involved. Earlier in the year, we were winning more games when that rotation was more involved.

"I kind of fell into the trap of Cristian Guzman tearing the cover off the ball and it became too hard not to put him in there. When I did that, I let a little rust get on Kennedy and Gonzalez. I think I have to avoid the temptation of playing the hot hand and keep Kennedy and the others involved. It seems to work better for us."

Walker hopes to play catch next week

WASHINGTON -- Nationals reliever Tyler Walker, on the disabled list with a sprained AC joint in his right shoulder, is hoping to start playing catch sometime next week. The club has not ruled out Walker coming back after the All-Star break. He hurt the shoulder while pitching against the Tigers last month.

Walker has done more than an adequate job for Washington, pitching in 24 games with a 3.57 ERA. He admitted that he was frustrated because he was pitching well before the injury.

"I was throwing the ball well," Walker said. "It's just a matter of getting healthy, getting out there and doing it again. I want to get back out there. It kills me that I can't go out there and be with the team. It is what it is."