“Every team in this league has had to test their depth at some point in this season,” Coach Ben Olsen said of shorthanded D.C. United, which will host Colorado on Sunday night to open a stretch of five games in 15 days. (Rob Carr/Getty Images)

A few weeks ago, Taylor Kemp was hoping just to be included on D.C. United’s game-day roster. David Estrada was not sure where his Seattle Sounders career was headed and Kofi Opare was receiving periodic starts for the Los Angeles Galaxy.

These days they are teammates in Washington, potential key elements in United’s effort to overcome a set of injuries and a suspension during the most hazardous spell of the MLS season.

Kemp, in his second year from the University of Maryland, is the probable starter at left back ahead of Sunday evening’s match with the Colorado Rapids at RFK Stadium — the first of five games in 15 days for the depleted hosts (11-7-4).

Acquired in trades nine days apart, Estrada and Opare are at the ready as part of a changing collection of reserves.

Until now, Coach Ben Olsen has not had to lean hard on his bench. Through the end of September, however, he might have to rely on almost the entire roster.

“Every team in this league has had to test their depth at some point in this season,” Olsen said. “We have been a little fortunate in the early part to not have to; now we are. We’ve prepared the best we could for it and now we’ll see how it goes.”

Kemp is the prime candidate to replace Chris Korb, who has been ruled out for a month after injuring a hamstring last weekend at Real Salt Lake.

Most of the other usual starters are available against Colorado (8-9-6), but injuries to several reserves and the heavy schedule will inevitably require secondary players to step into critical roles in the near future.

In addition to league matches, United is about to begin play in the 2014-15 CONCACAF Champions League, featuring clubs from North and Central America and the Caribbean. In the first of four group matches over two months, D.C. will host Waterhouse of Jamaica on Wednesday.

“We know August is a rough scheduling month, and even September,” said Kemp, who made his first start of the season two weeks ago in Houston. “We have a ton of games. Ben told the whole squad, ‘I am going to need everyone, so you’ve got to be ready.’ ”

Aside from Korb, starting center back Jeff Parke has been out for weeks with migraines and vertigo. Conor Doyle, a primary backup forward, and second-choice goalkeeper Andrew Dykstra were lost for the season with knee and Achilles’ tendon injuries, respectively.

Reserve forward Michael Seaton is recovering from a quadriceps ailment, while others are returning from minor setbacks. Starting striker Eddie Johnson is serving a two-game ban for kicking the ball at a fallen opponent last weekend.

The need for depth prompted the acquisition of Estrada for a 2017 third-round draft pick and Opare (plus a second-rounder next year) in exchange for swapping positions in MLS’s player allocation order.

Estrada, in his fifth pro season, scored five goals in 2012 but made one regular season appearance this year. The midfielder-forward shuttled between Seattle and loan assignments with the second-division Atlanta Silverbacks and third-tier Charlotte Eagles.

“I was having a hard time breaking into the lineup so it was exciting for me to come here,” said Estrada, who debuted with D.C. last weekend. “I saw it as a fresh start, and I think I am in a good situation right now.”

Opare, a second-year center back who started five matches for the Galaxy, has been in uniform the past three games for United but yet to play. Rookie Steve Birnbaum has partnered with captain Bobby Boswell since Parke first went down with a foot injury in early June and then began experiencing head problems.

“It’s an exciting challenge for us. We’ve got a little adversity now,” said Olsen, whose team has dropped two straight since winning four in a row.

“We’ll see how we respond to it. We knew we were going to hit a period [with] injuries or a bunch of games coming at us, [but] it’s part of the season. I am confident in the character of this group that we can get through this.”