D.C. United forward Freddy Adu won't play tonight against the MetroStars because of a knee injury. He'll also miss Saturday's match with Chivas USA and is almost certain to be sidelined the following weekend against the Los Angeles Galaxy.

However, Adu and club officials said yesterday that they don't believe his sprained medial collateral ligament, suffered in the first minute of last Saturday's 3-2 victory at Chicago, will have long-term implications.

"He's 16 years old, he'll be a pretty quick healer," team trainer Brian Goodstein said after overseeing Adu's strength and balance exercises while the team practiced at the RFK Stadium training grounds.

An MRI exam revealed a second-degree sprain but no cartilage damage. The team is hoping he will available for the U.S. Open Cup quarterfinal against FC Dallas on Aug. 24, although he might not be ready until early September.

Adu has missed only four regular season matches in two years, all in June while playing for the U.S. under-20 national team at the world youth championship in the Netherlands.

"I'm feeling much better than I did a few days ago," he said. "I should be back really soon. I'm doing everything they told me I couldn't do, which is funny -- like doing lunges and squatting all the way down without any pain."

Adu's injury comes at a time when both he and the club are in top form. Adu (second on the team with five assists) scored two impressive goals in recent weeks and exuded confidence on the attack while teamed with veteran forward Jaime Moreno.

In Adu's absence, United will likely turn to Santino Quaranta, who started on the right side of the midfield in Chicago and moved up front when Adu departed. Like Adu, Quaranta has also been playing his best soccer of the season of late.

With Quaranta at forward, Coach Peter Nowak would still have plenty of options in his healthy midfield corps, and he'll again have a full-strength back line with the return of rookie Bobby Boswell, who served a one-game suspension last weekend.

United (9-6-5) will try to maintain the momentum of a four-game unbeaten streak in league play (4-1-1 in all competitions) that has carried it to within four points of co-leaders New England and Chicago in the MLS Eastern Conference standings. The MetroStars (7-6-8) are close behind, trailing D.C. and Kansas City by just three points.

Fueling United's resurgence has been crisp combination play and a balanced attack, elements sorely missing much of the season. But Nowak expressed concern about his team allowing two late goals Saturday, which nearly wiped out a big lead.

"We're getting smarter, that's for sure," Nowak said. "It's still not perfect, we still have to work on a couple of things. We were winning 3-0 and we have to keep the lead and make sure nothing like that happens in the future. We put ourselves in a difficult spot and, for our confidence, it's not good to have a lead and then get shaky at the end."

Defensive reinforcement will come today, when Facundo Erpen is scheduled to arrive from Argentina. However, he won't be eligible to play until next week when the international transfer window opens.

United has also shown interest in an Argentine forward-midfielder, Francisco Guerrero, according to a source close to the player. Guerrero, who will turn 28 this month, starred for his country at the 1995 world youth championship, scoring a goal in the final against Brazil, and has played on the club level for Independiente in Argentina and Zurich and Basel in Switzerland.

It's unclear, however, whether MLS and United would be able to afford him. Team officials declined to comment.

United Notes: Quaranta missed practice and other players arrived late because of the major traffic back-up on Kenilworth Avenue yesterday morning. . . .

The team's charitable arm, United for D.C., will collect school supplies outside Gate A at each of the four home games this month. Fans who donate will receive a ticket voucher and promotional items. . . .

Defender David Stokes (ankle) remains sidelined.