As sides in the MLS labor impasse remained locked in negotiations Monday, D.C. United union representative Bobby Boswell said the players have made concessions on key issues.

“Our question now is, are they going to make any back toward us?” Boswell said. “The jury is still out on that one.”

With four days until the season is set to begin, union and management representatives met with federal mediators in Washington on the second of three consecutive days of scheduled talks. They met for about 11 hours Sunday and were prepared to work all day Monday and Tuesday, if necessary.

For the first time, team owners are participating in the discussions. FC Dallas’ Clark Hunt was among them Sunday and New England’s Jonathan Kraft was expected to arrive Monday. Numerous players from around the league are also present.

Teams have conducted training camp without a collective bargaining agreement but players say they will not start the season unless a new pact is struck. Free agency and compensation issues are at the heart of the matter.

“Ultimately, everybody wants to play, but it might not be a situation where we can play,” United midfielder Davy Arnaud said. “If it’s not something that is good for the players, we are not going to be able to play.”

Although no firm deadline exists, teams playing on the road this weekend are scheduled to begin traveling Thursday. The MLS opener is Friday, with Chicago visiting reigning champion Los Angeles. Without a deal, or signs of major progress, players are not expected to board their flights.

“We’re trying to find a deal and, with the tone [league representatives] came in with, they are trying to find a deal too,” said Boswell, who attended Sunday’s meeting and, after practicing Monday at RFK Stadium, headed to the second session. Teammate Chris Rolfe missed practice to join the talks Monday morning.

“Getting done is the hard part. I am not going to act like that is an easy task,” Boswell continued. “I am always optimistic. We have made a lot of concessions and we’re trying to keep the ball rolling. It’s in their court.”

Boswell declined to discuss specifics or what concessions were made by the union but said talks are proceeding cordially.

“People aren’t throwing chairs,” he said. “Some of it is philosophical but we’re all trying to hear each other out and make moves to get a deal done.”

Without it, MLS is facing the first work stoppage in the league’s 20-season history.

“We’re not naïve,” Boswell said. “We knew going into this that every [U.S. sports] league that has won free agency has won it through a work stoppage. We’re hoping to be that outlier.

“At the end of the day, we are soccer players and want to play soccer. The league is saying they want to see the first game kick off, but it’s easy to say that. Let’s make sure it happens.”