In year's past, D.C. United's first involvement in the U.S. Open Cup has usually come amid a busy MLS schedule. That's meant that head coach Ben Olsen opted to rotate his squad, keeping players fresh and giving other players an opportunity to prove themselves on the field.

This year, United's introduction to the tournament — on Wednesday at Audi Field against the Philadelphia Union — comes during a long break in MLS play. That should give Olsen a chance to play the starters, considering there won't be another league game for 12 days.

"We are going to put the best team [out] for Wednesday's game as possible," Olsen said on Monday after the team's practice. "But there are some absences with Gold Cup, Copa America, and some injuries."

The international absences are Paul Arriola with the USA and Junior Moreno with Venezuela. Chris Durkin, a crucial part to the U.S. U-20 side that lost in the quarterfinals to Ecuador on Saturday, was back in training on Monday. But the youngster is suspended for the game against the Union after picking up a red card last year, when the Black-and-Red bowed out of the tournament to Orlando City.

In addition, Russell Canouse and Bill Hamid weren't at practice on Monday. Nothing too much to worry about, according to Olsen, but the pair might not make the field on Wednesday.

"Russ and Bill have some little things that we'll have to make a decision whether they'll factor into the game Wednesday," said Olsen. "Nothing significant, but we might have to be smart with those guys."

There is some good news for United on the injury front, though. Joseph Mora, who has missed the past two months after breaking his jaw against Orlando, is back to full training with the team. Rookie defender Donovan Pines, who injured his knee last month, is days away from completely returning to practice. And Akeem Ward, who missed about 10 days, is back healthy as well.

Steven Birnbaum, who suffered a nasty head injury in the 1-1 draw against the San Jose Earthquakes on June 1, immediately passed the concussion protocol and seems poised to play against the Union. The only question for the center back is whether or not he'll have to wear a helmet to protect the stitches in his head.

"Just a cut, another cut on the side of my head. I am going to try to minimize those," Birnbaum said with a laugh on Monday. "I might have to wear a helmet for this game, we'll see if I get the stitches out before the game or not."

So it's possible that United could be missing four starters against the Union for the Open Cup on Wednesday. But otherwise Olsen might trot out a side featuring United's biggest stars, including Wayne Rooney and Luciano Acosta.

"It's important to keep rhythm and get better, and the first step is going out there Wednesday with the best group we can put together, and win a game," said the manager.