Dwayne De Rosario sprained the medial collateral ligament in his left knee while playing a World Cup qualifier for Canada. He will not need surgery but must sit out 10 to 12 weeks. (Ned Dishman/GETTY IMAGES)

D.C. United tried putting the best face on a rotten situation Thursday — a season-ending knee injury to Dwayne De Rosario that has jolted the club’s playoff outlook.

Coach Ben Olsen and the players pointed to the team’s wealth of attacking options, to roster depth and to the galvanizing effect after an emotional setback. They said the club’s playing philosophy and camaraderie, steeled by a long season, would remain intact.

But there was no getting around the loss of one of the league’s most productive, influential and driven players. Since his arrival in June 2011, the 2011 MLS most valuable player has been the centerpiece of United’s rebuilding efforts and the one player who could alter a match with the flick of his foot.

On Tuesday, while playing for Canada’s national team in a World Cup qualifier in Panama, De Rosario sprained the medial collateral ligament in his left knee. He will not need surgery but must sit out 10 to 12 weeks.

Six weeks remain in the MLS regular season, followed by a possible month of playoffs. Even with a postseason surge, United isn’t holding out hope of him returning this fall.

“Absolutely gutted,” De Rosario, 34, wrote on his Twitter page. He will also miss Canada’s crucial World Cup qualifiers against Cuba and Honduras next month.

After the initial sting, United began looking ahead.

“It’s bad news, but it’s over with,” Olsen said. “What changes is you don’t have a guy out there who can do really special things at any given moment. I’m looking for some other guys to raise their game. We are under it a little bit. We have a pressure situation here.”

Few in the league thrive better under pressure than De Rosario, a forward-midfielder who has recorded 20 goals and 19 assists in 42 regular season starts since moving to Washington from the New York Red Bulls.

The team captain entered this week tied for second in MLS with 12 assists and has scored seven times, three behind club leader Chris Pontius. He missed one game with injury, entered as a substitute in another and has played 2,195 of 2,430 minutes to rank second in time served this year.

The loss of De Rosario was bad enough; the timing made it worse. United is in a 2-5-2 rut, a downturn that jeopardizes a season that seemed on pace to snap a five-year playoff drought. D.C. (12-10-5) is in sixth placein the Eastern Conference and a point out of the last postseason berth.

With the MLS roster deadline at the end of business Friday, United officials have had little time to pursue a trade. The international signing period closed last month. The club doesn’t have much salary cap space, either.

“Not too many teams are looking to give up 100-goal scorers for a fourth-round draft pick,” Olsen said. Last month, De Rosario became the seventh player in MLS history to post 100 regular season goals.

“This is who we are and everybody has to give a little bit more,” Olsen continued. “It’s doable. This is not an excuse. We’re not looking for any pity parties.”

De Rosario’s injury came one year and one day after Pontius suffered a season-ending broken leg, an absence that contributed to a 1-6-2 swoon. Despite the similarities, Olsen believes he has a deeper and mentally tougher squad.

He will, however, need several players to help fill the void. Forward Maicon Santos (seven goals) has returned from a foot injury and rookie midfielder Nick DeLeon has regained his form after a midseason slump.

Forward Lionard Pajoy has played well in five straight starts but scored just once. Striker Hamdi Salihi, who fell out of favor in July, might get another look.

Central midfielder Branko Boskovic will inherit greater playmaking responsibility — but also attract additional defensive attention. Without De Rosario alleviating pressure, United could have trouble generating scoring opportunities.

On the bright side, United’s next five opponents have losing records. The New England Revolution (7-14-7) will visit RFK Stadium on Saturday night.

“It’s a big blow,” defender Brandon McDonald said, “but we can’t dwell on it.”