With the regular season winding down and D.C. United emerging from a summer rut, Ben Olsen is largely done experimenting with players and formations.

Except in the case of injury or suspension, the lineup and the primary substitutes seem set.

There is, though, one position worthy of discussion: striker.

Olsen prefers to start one, not two. He is, however, equipped with a pair of proven scorers, Wayne Rooney and Ola Kamara.

Since the latter’s arrival in mid-August, it hasn’t been an issue. Rooney was saddled with injuries and a two-game suspension for a red card.

When the Englishman returned for Sunday’s 1-0 victory at Portland, he was supposed to come off the bench and Kamara was slated to start — a reward for scoring twice at Montreal the previous outing.

On the eve of the game, however, Kamara’s tight hamstring rendered him unavailable.

That lingering ailment — Kamara did not practice in full Wednesday — will allow Olsen to maintain the status quo Sunday against the Seattle Sounders at Audi Field.

When both are healthy, Olsen will have to decide.

“Looking to the future? I don’t know,” he said. “You could probably make a guess on what’s next, but we haven’t made any decisions, and these are always long weeks.”

Given the health of the players, it’s Rooney’s job to lose, even though he has gone two months and five matches without a goal.

United (12-10-9, 45 points) has struggled in the attack as a whole: Its 40 goals are the fewest among teams currently in the 14 playoff spots and, entering Wednesday’s action, tied for fourth fewest in the 24-team league. The victory at Portland was fueled by a first-half own goal.

Since his fourth game last summer, Rooney has started all but one in which he was available. United signed Kamara before the transfer window closed last month to provide depth this year but mostly to help fill a large void next season: Rooney will cut short his MLS tenure this fall to become a player and assistant coach for Derby County in England’s second flight.

While Rooney has not been in top form this year, the blame for United’s ills run deeper: The attack in general has sputtered, and ineffective playmaker Luciano Acosta lost his starting job.

“I’m sure Ben has got different ways to play, whether that is me or Ola up top,” said Rooney, who leads the team in goals (11) and assists (seven). “That is Ben’s decision. I have to keep trying to be ready to play and be there, whether that means playing [striker] or a deeper position.”

Along those lines, one thought is to start both Rooney and Kamara, with Rooney as a withdrawn forward or attacking midfielder. But with the playoffs nearing, Olsen is comfortable with the one-forward formation and the accent on defense. (United is fourth in fewest goals conceded, and Bill Hamid is second in shutouts with 11.)

Rooney and Kamara did start together on the front line Aug. 21 during a 2-1 defeat to the New York Red Bulls. Because of Rooney’s absences, that experiment did not continue.

“We made that decision a few weeks ago where we said, ‘Okay, we have to drill down on who we are and who we are going to be,’ ” Olsen said. “It’s important to have a structure with the ball and without the ball that everyone is really well rehearsed in at this point in the season.”

He added, though, “That’s not to say we’re not going to adjust at times throughout the games and to the opponent.”

Notes: United thought it had scored a second goal in Portland, when a deflection appeared to cross the goal line for a two-goal lead. Video assistant referee Ricardo Salazar, however, did not recommend a full review to on-field ref Drew Fischer.

“It’s not conclusive, and it should be conclusive,” Olsen said. “We have the ability and the technology is out there to make it conclusive. … Just got done [watching] U.S. Open tennis; they seem to have it down pretty well.”

Goal differential is the second tiebreaker after total victories and could play a role in deciding home-field advantage in the first round of the playoffs. United is even with fourth-place Toronto on points and victories but behind by two in goal differential. …

Forward Quincy Amarikwa missed training Wednesday for personal reasons.

Read more: