For the second consecutive week, a D.C. United player on the brink of joining the active roster for the first time this season has been sidelined for an extended period because of additional problems with a previous injury.

Forward-midfielder Eliseo Quintanilla, fifth on the team in scoring last year, will undergo surgery on his right leg this week to re-set the fibula, which he had broken during preseason workouts, United technical director Dave Kasper said yesterday.

Quintanilla, a 21-year-old Salvadoran, will probably be sidelined an additional three months, all but ending his season. Last year he started 12 games and had three goals and three assists.

"It just didn't heal properly and he was experiencing some pain," Kasper said. "It's a tough blow for Eliseo."

Last week Brazilian forward Thiago Martins, who had just recovered from offseason surgery on the anterior cruciate ligament in his left knee and was cleared to play, re-injured his knee and will have surgery soon to repair a meniscus tear.

During the operation, doctors will be able to determine whether Martins has additional ligament damage. If he does, he will have to sit out another six months. Otherwise, the team is hoping he could return in six weeks.

Meantime, starting defenders Ryan Nelsen and Bryan Namoff, who have abdominal strains, didn't participate in regular workouts yesterday and appear questionable for Saturday.

Namoff has missed the last two matches; Nelsen started in last Saturday's 0-0 tie with the Colorado Rapids, but left at halftime because of his injury, which he initially suffered several weeks ago.

Help Wanted

With injuries, inadequate depth on defense and a dearth of goal-scoring, United has begun looking for help.

Uruguayan defender-midfielder Alejandro Curbelo, 30, who sparked Alianza to the Salvadoran league title this summer, began a tryout yesterday. Curbelo has made appearances for Uruguay's national team, most notably at the 2001 Copa America.

Also in camp is Tim Lawson, a 28-year-old midfielder-forward who plays for SV Elversberg in Germany's Third Division. He starred at the University of Washington with current United defender Brandon Prideaux.

United is also continuing to look at Bolivian midfielder Roland Aguilera, who arrived last week from the minor league Virginia Beach Mariners.

Kasper said the team has had informal talks with other players about coming in for formal tryouts but declined to identify them.

United has gone 265 minutes without a goal and is ninth among 10 MLS teams in goals per game with an average of 1.00. (Colorado is last at 0.60.)

Convey, Stewart Away

Midfielders Bobby Convey and Earnie Stewart are away all week with the U.S. national team at training camp on Long Island and will miss Saturday's match against the Columbus Crew at RFK Stadium. The American squad is preparing to face Grenada on Sunday on the Caribbean island in the finale of their World Cup second-round qualifying series.

Meantime, 15-year-old forward Freddy Adu has joined the U.S. under-20 squad for tonight's friendly against Brazil in Fort Lauderdale, Fla. However, he will be available for United on Saturday. D.C. Coach Peter Nowak was scheduled to fly to Florida yesterday after practice to attend the U.S.-Brazil match. . . .

Several United players and staff members helped with a Habitat for Humanity project at 54th and Clay streets in Northeast yesterday.

Eliseo Quintanilla (20) will have his fibula re-set; he had been close to return after breaking his leg in preseason.