WASHINGTON -- Clayton Kershaw experienced a setback in his recovery from a lower back injury, and the return of the Los Angeles Dodgers' ace pitcher remains uncertain.

Kershaw, on the disabled list with a mild disk herniation, has not pitched since June 26 at Pittsburgh. He suffered his second loss of the season in that outing, when he gave up four runs on nine hits in six innings. A day later, he was being examined for back issues that were being downplayed at the time, but he ended up on the disabled list by the end of the week.

The Dodgers felt their top pitcher might be ready for a return on the current road trip that ends Sunday at St. Louis, but discomfort after a simulated start Saturday at Dodger Stadium has nixed those plans.

"Clayton, after he threw that live session, the next day Sunday didn't feel great," manager Dave Roberts said before Tuesday's series opener against the Nationals. "I think that at that point and time he let us know that we had to be a little more on the cautious side.

"I don't know if it's a step back, but we're going to let the back pain subside and see where we go. So as far as his return ... uncertain."

Roberts would not say if Kershaw's condition is back to where it was when he went to the DL, or if it is worse. His simulated start came 20 days after his last outing in the major leagues, so if his condition is right back where it started, another three weeks could go by before he is ready to test the back again. That would move the timetable into the second week of August, and even further for a return to a major league mound.

The Dodgers have managed to play winning baseball without Kershaw. They are 11-6 in the left-hander's absence, but their scramble with the rotation goes beyond their three-time Cy Young Award winner. Brett Anderson (back) has been out since spring training and Alex Wood (elbow) has been out for most of the season. Before the All-Star break, Hyun-Jin Ryu returned from shoulder surgery for his first start since 2014, but he returned to the disabled list Tuesday with elbow tendinitis.

The Dodgers will call rookie Julio Urias back to the major leagues for a start Thursday at Washington. It means their current rotation consists of Scott Kazmir, Bud Norris, Urias, Brandon McCarthy and Kenta Maeda.

It could push the Dodgers toward seeking starting pitching at the Aug. 1 non-waiver trade deadline. The club figures to be even more cautious with its star pitcher than it had been.

"With the back, you have to be extra sensitive, and obviously it's Clayton," Roberts said. "When you're dealing with a back there is some concern, certainly. We're just hoping that in the coming days there is some improvement."

The Dodgers entered play Tuesday as the top team in the National League wild-card standings, one game ahead of the Miami Marlins and two ahead of the New York Mets. But both teams have gained ground in recent days.

"Clayton will do everything he can to get back," Roberts said. "We're better when he is active, obviously. It's something we have to deal with and we have to continue to try and win baseball games."