Atilano was put on the disabled list Friday, retroactive to Wednesday, with bone chips in his right elbow.
Detwiler will make his season debut on Sunday against the Brewers and most likely will pitch no more than five innings. Detwiler last pitched Wednesday for Double-A Harrisburg, going seven shutout innings against New Britain.
During his eight rehab starts, Detwiler is a combined 2-2 with a 2.27 ERA for Class A Potomac and Double-A Harrisburg.
The Nationals are not concerned that Detwiler will pitch on three days' rest, according to manager Jim Riggleman.
"We will monitor him a little closely," Riggleman said. "I'm not sure how far we will let him go. He is the guy who is throwing as good as anybody down there. We feel he could handle it fine."
Detwiler has missed most of this season after undergoing surgery to repair a labral tear in his right hip last February.
The procedure was performed in Vail, Colo., by Dr. Marc Philippon, the same doctor who performed hip surgery on Yankees third baseman Alex Rodriguez and former Nats closer Mike MacDougal.
Detwiler started feeling pain while throwing the baseball before Spring Training started. Detwiler then went to the trainers and had an MRI. The trainers didn't like what they saw, so Detwiler went to Colorado to see Dr. Philippon, who confirmed surgery was needed.
Detwiler, the Nationals' first pick in the 2007 First-Year Player Draft, went 1-6 with a 5.00 ERA in 15 games with Washington last season, but had a 1.90 ERA during the month of September.
"Last year, when he was with us in September, I think we saw a little more confident guy," Riggleman said. "He threw a lot of good ballgames for us the last five weeks of the season. I'd like to see him go out there and do what he did in September -- see if he can do it here in July and August. He is a guy the organization is counting on. He has gone through some trouble that everybody seems to go through -- injuries. Once those pitchers get that behind them, they seem to get their careers going."