“There’s a spot or two we can fill, but for the most part, this is our group,” Olsen said Monday. “I’ve got no [roster] decisions to make right now.”

The most recent decisions: Offer a contract to former Montreal left back Maxim Tissot and release goalkeepers Charlie Horton and Matt Sanchez (Loyola, Md.), defenders Suli Dainkeh (South Lakes High School, University of Maryland) and Jo Vetle Rimstad (Radford), and midfielder Kyle Porter.

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United does have some cash and roster space in reserve for likely use in the summer transfer window.

A few new trialists might join the delegation for the second phase of training camp starting late this week in Clearwater, Fla., but with the core of the squad returning from last year’s playoff team and a few impactful additions, Olsen has been able to concentrate on assembling the starting lineup and identifying the most effective combinations.

Will Bobby Boswell or Sean Franklin partner with Steve Birnbaum in central defense? Does Franklin or Nick DeLeon start at right back? Is rookie midfielder Ian Harkes ready to start? What to do with incoming forward Jose Guillermo Ortiz?

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“It’s a bit of a puzzle,” Olsen said. “It’s figuring out who works with who. The focus right now is mixing up as many combinations as possible with the understanding everyone is going to play with each other throughout the year and contribute.”

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The most intrigue falls on the back line. Birnbaum and left back Taylor Kemp are locked into starting jobs. Olsen has tested Franklin, a natural right back, in the middle and continued gauging DeLeon, a natural attacker, on the right corner.

Asked whether DeLeon is a defender or midfielder this year, Olsen said: “Right now, he is a right back. I see him growing in that position over the course of the year. Could be Sean, could be Nick. It’s certainly one of those two. I really like both as options. It’s rare to have depth at that spot.”

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Franklin has a better understanding of the position and is more defensively sound. DeLeon is five years younger and offers greater ability to join the attack from a deep, wide position.

DeLeon did not play on the back line regularly until late last season, when Franklin was recovering from injury.

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Even if DeLeon wins the battle, Franklin remains a contender to start in central defense. As at right back, Olsen sees two players with different qualities. Boswell, who turns 34 next month, has started 350 regular season games in his 12-year MLS career — invaluable experience at a critical position. Franklin, a starter at outside back since his second season in 2009, provides greater pace.

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“They are both experienced defenders in this league,” Olsen said.

The other spot to watch: the central midfield job in tandem with playmaker Luciano Acosta. Jared Jeffrey is the incumbent, but Harkes, college soccer’s Hermann Trophy winner last season, has made an early impression.

“He’s a super-talented kid,” Olsen said, “and each day he seems more comfortable with the pace of the game and the relationship” with other midfielders.

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Upon signing Harkes to a homegrown contract last month, United needed to determine whether he was best-suited for an advanced role alongside Acosta or as an understudy to veteran Marcelo Sarvas in defensive midfield. Olsen said it has become clear Harkes is best further up the field, where he’s more engaged in the attack.

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Olsen plans to retain the 4-1-4-1 formation that yielded late-season success last year: four defenders, a defensive midfielder, two central midfielders flanked by two wings and a lone striker.

Patrick Nyarko and Lloyd Sam are the returning starters on the flanks, and Patrick Mullins is the incumbent at striker. But Ortiz, 2016 leading scorer Lamar Neagle and free agent signing Sebastien Le Toux are adept up front or out wide.

“The players sense there is a real competition for playing time, and it’s bringing out the best in the right way,” Olsen said. “There’s still an understanding that we are a group and whoever ends up in the starting lineup, everyone will and needs to contribute for us to have success. That spirit is there right now.”