Chris Rolfe, left, against Houston’s David Horst in May at RFK Stadium. (By Rob Carr — Getty Images)

Chris Rolfe, D.C. United’s third-leading scorer, will miss six weeks after fracturing his left forearm in practice, the club announced Thursday.

Rolfe, who is also second on the team in assists, underwent surgery at George Washington University Hospital on Wednesday night.

He was injured trying to brace himself on a fall during a workout Wednesday morning at the RFK Stadium training grounds. He was immediately taken to see the team doctor, who consulted with a specialist.

Rolfe will wear a cast for about two weeks, then a brace. At that point, he can resume conditioning work. He is to avoid contact for six weeks and will not be able to play during that time, General Manager Dave Kasper said.

The timetable leaves United without one of its most important attackers for almost the remainder of the regular season. D.C. (14-8-4) has eight games left, culminating Oct. 25. Barring complications, Rolfe (six goals and six assists in 21 appearances) should return for the Oct. 18 home finale against the Chicago Fire. Aside from the MLS matches, Rolfe will also miss two of the remaining three CONCACAF Champions League group games, although he might have skipped those anyway as Coach Ben Olsen provides playing time for others during busy stretches on the calendar.

“You never want to lose anyone,” Kasper said, “but we have been fortunate with the strength of our depth.”

Luis Silva performed extremely well when leading scorer Fabian Espindola missed two months with a knee injury this summer and United has filled shorter-term voids at various points.

With Rolfe out, Olsen will probably turn to veteran midfielder Lewis Neal (seven starts) at Vancouver on Saturday. Kyle Porter, Alex Caskey and forward Eddie Johnson are also in the mix to fill Rolfe’s slot on the left wing.

In addition, Chris Pontius, an all-league performer two years ago, is close to making his season debut after recovering from a hamstring injury. Pontius’s natural position is on the left side of the attack. He has been training at full speed for a few weeks and might rejoin the game-day roster in the coming weeks, Olsen said.

Rolfe’s injury will not alter United’s plans ahead of the Sept. 15 roster freeze, Kasper said. The team had been working on a acquisition before Rolfe went down. Kasper declined to identify the targeted player, but an unidentified trialist was practicing with the club this week. With the international transfer window passed, MLS teams are only permitted to sign free agents, make trades and acquire other domestic players.