He appears to have a tough matchup awaiting him in the Washington Nationals, who go for a season-best fifth consecutive win Saturday night at Petco Park.
Cashner (2-5, 2.35 ERA) is set to take the mound for the first time since May 13, when he yielded one run over seven innings in a 2-1 win at Cincinnati. The right-hander didn't receive a decision in that game and is 0-4 with a 3.41 ERA in his last five outings.
While on the shelf, Cashner has been tweaking the grip and release on his slider, which may have caused the initial pain.
"I'm just kind of moving my fingers on the ball where I can't wrap it, (so I) stay behind the ball," he told the Padres' official website. "Hopefully we don't miss a beat when I come back."
Cashner, who has allowed two earned runs or fewer in all but one of his nine starts this season, has been backed by a combined three runs of support in his five defeats. He allowed four runs - two earned - over six innings in a 4-0 loss at Washington on April 26, dropping to 0-2 with a 9.00 ERA in his last two starts in the series.
Cashner will try to cool off a Nationals team that's won six of seven, including its last four by a 25-6 margin. After sweeping Philadelphia, Washington (31-28) kicked off a 10-game road trip with Friday's 6-0 victory. Anthony Rendon hit a two-run homer and Tanner Roark combined with Ross Detwiler on a three-hitter.
Rendon has hit .414 with four homers, eight RBIs and nine runs over the last seven games. He's 9 for 26 with two homers and eight RBIs in his last six versus San Diego (27-34).
The Nationals give the ball to 25-year-old rookie Blake Treinen (0-2, 1.40). The right-hander has dropped each of his two starts despite a 1.69 ERA while receiving a combined one run of support.
In his last start, Treinen allowed two runs, four hits and five walks over 5 2-3 innings in a 3-1 defeat at Pittsburgh on May 22.
"I've got to cut down on the walks and try to keep us in the game better by getting out of the situations I've been getting myself into," Treinen said after throwing 63 of his 102 pitches for strikes.
He was better in his only appearance since that day, throwing two scoreless innings of relief without a walk last Friday against Texas.
San Diego has hit .104 and been outscored 26-8 in dropping four of five this month. The Padres have already been shut out nine times, matching their total from all of last year.
"You have to keep your nose to the grindstone and keep working," manager Bud Black said. "There is no magic formula to this. You keep working, you keep busting your butt in the cage, you keep watching video, you keep your confidence, you keep telling yourself you're going to have good at-bats, you stay together as a team, you hang in there in the hopes that it will turn."
Third baseman Chase Headley is 3 for 28 with 11 strikeouts during an eight-game stretch, and Carlos Quentin is 0 for his last 16.
San Diego placed second baseman Jedd Gyorko on the 15-day disabled list before Friday's game due to plantar fasciitis in his left foot. He's hitting .162 with five homers and 24 RBIs in 56 games.