Andy Najar received a red card in D.C. United’s playoff opener and will miss the Eastern Conference finals. (Patrick McDermott/Getty Images)

D.C. United’s Andy Najar will miss the MLS Eastern Conference finals after receiving a two-game suspension for throwing the ball at the referee during the playoff opener last weekend.

He had already served an automatic one-game penalty Thursday, missing United’s 1-0 victory at New York. The league’s disciplinary committee punished him further, a decision that ends his season unless United advances to the MLS Cup on Dec. 1.

Commissioner Don Garber denied an appeal by the players’ union Friday. Najar was also fined an undisclosed amount. In announcing the ban, MLS said “Najar’s conduct put the league in disrepute.”

In its first appearance in the conference finals since 2006, second-seeded United will play the No. 5 Houston Dynamo on Sunday afternoon at BBVA Compass Stadium and then a week later at RFK Stadium. Like the previous round, the two-game series is decided by total goals and, if necessary, overtime and penalty kicks.

Najar, 19, isn’t the only young United starter who will serve a suspension this weekend. Goalkeeper Bill Hamid, 21, received a red card in the second half Thursday, his second ejection of the season. He is not expected to face additional sanctions.

While Hamid was tossed for taking down Kenny Cooper on a breakaway, Najar was disciplined for petulance. Upset about being given a yellow card for a midfield tackle, he hurled the ball underhanded at Jair Marrufo, who immediately reached for the red card.

“While we understand the league spent considerable time reviewing the incident, as it was a difficult one, we’re disappointed with the decision to punish Andy for a total of three playoff games,” United General Manager Dave Kasper said.

“It won’t, however, have an effect on this group,” he added, referring to United’s adaptability during trying circumstances this fall.

Four others were disciplined in the regular season for similar behavior: FC Dallas’s Brek Shea (three matches) and Vancouver’s Barry Robson (one) for kicking the ball at an assistant referee; Los Angeles superstar David Beckham (one) for doing the same toward the head ref; and Galaxy teammate Mike Magee (one) for throwing the ball in the direction of an official.

Najar, an attacking winger for the majority of his three-year pro career, has been a revelation at right back since late August, when injuries prompted defensive changes. His overlapping runs and clever footwork have added an explosive element to the attack.

Najar’s suspension frees him to play for the Honduras national team in a friendly Wednesday against Peru at, coincidentally, BBVA Compass Stadium.

In his absence Thursday, Robbie Russell returned to the lineup and set up Nick DeLeon’s goal in the 88th minute. Russell had been United’s first-choice right back at the start of the year but was sidelined by a foot injury for two months. Since his return in mid-September, he had played just 12 minutes in three appearances.

In the finale against New York, though, Russell was composed and effective. He is expected to retain the job while Najar sits.

“Robbie is an old pro,” Coach Ben Olsen said of United’s most-experienced postseason player. Russell made 12 playoff appearances the previous four years with Real Salt Lake.

Hamid’s role will be filled by Joe Willis, who stopped a penalty kick in the New York finale after replacing the club’s expelled starter.

Meantime, United is monitoring the fitness of two other players. Chris Korb, the starting left back for two months, missed Thursday’s game with a hamstring injury. Lewis Neal filled in admirably but is a natural midfielder.

The big question is whether Dwayne De Rosario will return to active duty. The 2011 league MVP has been sidelined since Sept. 10 with a sprained knee but resumed workouts last week and is cautiously optimistic about facing his former club – if not in the opener, then the second game.

“I’m still taking it one step a time,” he said. “This is the playoffs and there is no mercy. I want to be in a situation where I am ready and can really help these guys out. I’ll sit down with the coaches and see where I am and continue to work on it. I’m with these guys, on or off the field.”

United notes: The club usually flies commercial, but because of the quick turnaround between rounds, it took a charter to Houston from the New York area Friday afternoon. . . . In the Western finals, the third-seeded Seattle Sounders will visit the No. 4 Los Angeles Galaxy on Sunday evening and then host the defending champions Nov. 18.