As the number of concussions accumulated over his career, Patrick Nyarko began to change the way he played soccer.

“In the past, I would go into anything,” he said. “When the ball was on the ground, I would throw myself forward. I like winning possession for my team, whichever way I can. Sometimes I would risk my health when I did that, but that’s how I played. I went into riskier stuff.”

Even a different approach, though, cannot prevent every potential head injury. Early in D.C. United’s MLS opener at Los Angeles two weeks ago, the attacker took a blow from behind, a head-to-head knock. It did not require a game stoppage or treatment. He was fine. Play continued.

A mild headache came on later but he was not dizzy or nauseous, common concussion symptoms. At halftime, though, he asked for pain reliever and, subsequently, underwent concussion protocol. Nyarko, 30, was done for the day with what was diagnosed as his fifth concussion since 2008.

“The doctors know the symptoms to look for, but against L.A., I didn’t feel it was a concussion,” he said. “Obviously, they are the experts. I am not disputing it. I think I could have played on.”

After skipping last weekend’s match at New England, doctors cleared him to resume training Wednesday. He is likely to suit up for Sunday’s home opener against the Colorado Rapids at RFK Stadium.

Concussions are a growing issue in all of sports, and perhaps no soccer team has had to treat as many as United. Over a decade, Alecko Eskandarian, Bryan Namoff, Josh Gros, Devon McTavish and Davy Arnaud were forced to retire because of head trauma. Two weeks ago, Arnaud ended a 14-year career after struggling for six months with symptoms.

“It’s bad we’ve seen so many,” Coach Ben Olsen said. “But with that comes a lot of experience and awareness about it. We have a good group of trainers and doctors who know the right way to go about this stuff.”

Nyarko, a former Virginia Tech star who joined United this winter after eight seasons with the Chicago Fire, suffered his first concussion late in his 2008 rookie season on a head-to-head incident against Chivas USA.

Two years later, he took a knee to the head against the Columbus Crew. In 2011 and 2013, there were head to heads against Colorado and D.C., respectively.

“A couple have been real minor,” he said. “With my past, we treat it with a lot more sensitivity and make sure everything clears before I get back” on the field.

The long-term consequences of multiple concussions, and whether they lead to conditions such as chronic traumatic encephalopathy (CTE), are the subject of intense medical research and studies.

Does Nyarko’s concussion history concern him about his future well-being?

“It does and doesn’t,” he said. “With the experience that I have, I know when it’s bad. Obviously, with the concussion count, when it mounts, it becomes a problem in later life, as documented in other leagues, other sports. I understand that. But I am pretty confident in the fact that I know when there is a concussion.

“It’s definitely a concern, but it’s more about prevention.”

This month’s head injury was his first in 2 ½ years. In a 2013 U.S. Open Cup semifinal against United, he went up for a header and, he said, “I knew I was going to get crushed afterward.”

Today, Nyarko said, he probably would not challenge for that ball in the same way. “With age, you grow up, and with experience, you grow up a little bit,” he said.

In this year’s regular season opener, United recycled the ball back into the penalty area after a corner kick. Nyarko lined up to flick the ball. From behind, Galaxy defender Daniel Steres’s head crashed into his.

In the same game, D.C. defender Steve Birnbaum was bloodied by a head-to-head collision with Steres in the first half. Treated on the field for several minutes, Birnbaum passed concussion protocol, had his head wrapped in a bandage and returned to action.

Though his collision turned out to be minor, Nyarko is mindful of the dangers associated with head injuries.

“You catch yourself thinking about it a little bit, especially watching TV and a feature [about concussions] comes on,” he said. “You become interested, but on the other hand, it’s about how you get through your career without the effects. You learn to make sure it doesn’t happen, and if it does happen, you take the appropriate measures to come back, take the longest time you need to make sure the brain is healed.

“Because they say the next hit is the worst one that could knock you out for a long time.”

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D.C. United vs. Colorado Rapids

Where: RFK Stadium.

When: Sunday at 5 p.m. ET.

TV: ESPN2.

Records: United 0-1-1, 1 point; Rapids 1-1-0, 3 points.

D.C. probable starters: GK Travis Worra: Ds Sean Franklin, Bobby Boswell, Steve Birnbaum, Taylor Kemp; MFs Patrick Nyarko, Marcelo Sarvas, Nick DeLeon, Chris Rolfe; Fs Luciano Acosta, Lamar Neagle.

Colorado probable starters: GK Zac MacMath; Ds Mekeil Williams, Jared Watts, Axel Sjoberg, Marc Burch; MFs Dominique Badji, Micheal Azira, Sam Cronin, Dillon Powers, Marco Pappa; F Kevin Doyle.