Midfielder Andy Najar, 18, has not played much thus far this year after he was MLS rookie of the year last season. (JOEL RICHARDSON/FOR THE WASHINGTON POST)

With D.C. United trailing the New York Red Bulls by two goals in the second half last week, Coach Ben Olsen turned to his bench.

First, he summoned midfielder Branko Boskovic to build possession. Then he beckoned forward Joseph Ngwenya for a physical presence. Finally, with United failing to dent the deficit, Olsen called on Santino Quaranta for striking prowess.

Meantime, United’s most celebrated and dynamic player last season, MLS rookie of the year Andy Najar, sat and watched — a recurring situation in recent weeks.

After starting the first two regular season matches, the 18-year-old midfielder has failed to crack the opening lineup. He entered in the second half of two games, missed one because of illness — he probably wouldn’t have started anyway — and was left out against the Red Bulls.

Najar’s absence has mystified fans and league observers alike: Why can’t a technically gifted player hold down a starting job for a club seeking to rebound from its worst season ever?

“I have no doubt in my mind Andy is going to be a great player for us, and he’s going to be a great player again this year,” said Olsen, who is expected to select Najar on Tuesday night for a U.S. Open Cup qualifier against the New England Revolution at Maryland SoccerPlex.

“His job is to use the games he has to show me that he’s ready to go when called on.”

As far as anyone around the club can tell, there is no rift between the animated coach and painfully shy player. After an Open Cup match against Philadelphia early this month, Olsen saluted Najar’s influential play and, over the past year, has spoken highly of him and his future.

But in assessing his options for league matches, Olsen has gone in a different direction of late. Quaranta and Boskovic manned the flanks at Colorado. Quaranta and Chris Pontius played the subsequent match against Los Angeles. Pontius and Fred received the nod against Toronto, a 3-0 away victory that earned them an encore against the Red Bulls.

“There is a lot of competition [for playing time in midfield] and my job is to just keep working hard to earn a spot,” said Najar, who started 22 of 30 league matches last year and was the club’s co-leading scorer with five goals. “Obviously, those are the coach’s decisions and all I can do is work hard.”

The revolving lineup hasn’t affected just Najar. In the first five matches, Olsen started a league-high 22 players.

“We are not always going to have the starting 11 week in and week out,” Olsen said, accentuating roster depth. “It keeps guys motivated, it keeps them on their toes. It can go the other way: Maybe there’s not a rhythm as much as you’d like. But overall, it’s fairly healthy so far.”

To some extent, Najar has himself to blame. He didn’t maintain fitness over the winter and arrived at training camp a step behind. His new-found fame seemed to dent his concentration.

Outside forces also contributed as pressure built to choose an international career: Commit to his native Honduras or wait years for U.S. citizenship and perhaps a national team invitation. (He eventually chose Honduras.)

Olsen stuck with Najar at the start of the season before shuttling him out of the lineup. “My message to the guys [is]: ‘If you’re out and someone comes in, it’s their job to keep the job,’ ” Olsen said.

Along those lines, Olsen’s message has been consistent: United is a work in progress and will require months to forge an identity. In the long run, Olsen said, Najar is very much in his plans.

The scarcity of playing time could affect Najar’s chances of playing for Honduras this summer. The roster for the CONCACAF Gold Cup, which will be held in June, is close to being finalized, and players not appearing regularly for their club face exclusion.

For now, however, Najar’s focus is on United, and earning his way back onto the field.

“I try to maintain a positive attitude,” he said, “and show what I am capable of doing.”

United notes: Pat Onstad, the goalkeepers coach who came out of retirement during a preseason injury crisis, will return to the lineup Tuesday, Olsen said.

Onstad, 43, started the first three league matches before yielding to Bill Hamid three weeks ago. With two games in four days, Hamid will prepare for Friday’s league match at Houston. . . .

Tuesday’s winner will play at Sporting Kansas City next month for a round-of-16 berth in the U.S. Open Cup, a 97-year-old tournament involving clubs from all levels of American soccer.