When Emiliano Dudar awakened, he asked his wife to call a taxi. The match was going to begin soon, he insisted, and his Swiss soccer club, BSC Young Boys, was expecting him at the stadium.

Except the match against visiting Basel in September 2010 had been over for four days. And Dudar had played in it — the first 30 minutes anyway, before the back of a teammate’s head cracked his nose and knocked him unconscious an instant before the left side of his skull struck the artificial turf with a sickening thud.

The Argentine defender was still out cold when he was transported to a hospital in Bern. Fearing serious injury, doctors induced a coma to allow his brain to heal from the severe concussion.

“Even now, I only remember spots of the game prior to the accident,” D.C. United’s new center back said through an interpreter this week. “The things I remember are walking onto the field, saying hello to the opponent, certain situations. The rest of the game is missing.”

Dudar, now 30, spent four weeks in the hospital, underwent a battery of tests and needed several months to recover. He returned to regular duty in February 2011. He said he hasn’t experienced any complications since, but when United took interest in him this winter to reinforce its back line, the MLS club proceeded with caution.

D.C. United defender Emiliano Dudar was in a coma for four days in 2010 after suffering a head injury in a game. (John McDonnell/The Washington Post)

After all, in recent years, three prominent United players — Alecko Eskandarian, Bryan Namoff and Josh Gros — were forced to retire in the prime of their careers because of head injuries. Several others have been sidelined for extended periods with concussions. This past offseason, reserve defender Devon McTavish, 27, stepped away after missing most of 2011 with concussion symptoms.

So before finalizing a contract with Dudar, United consulted with Young Boys doctors and reviewed his medical history (his concussion was the only one he is known to have suffered). When he arrived in Washington, the club sent him to a neurologist and physical therapist. It administered a neurocognitive test that assessed, among other areas, attention span, memory and judgment. A psychologist then evaluated the results.

“We’ve had so much experience [with concussions], we know these tests in and out, we know the doctors in and out, we know the best guys to see,” Coach Ben Olsen said. “They gave him a passing grade.”

In scouting Dudar, United watched video of him before and after the incident and didn’t notice a drop in performance. What club officials did notice was a 6-foot-4 defender with good footwork, aerial dominance and leadership qualities.

He has a deep, booming voice — using mostly Spanish — and assertively directs teammates to cover specific ground.

With the season opener against Sporting Kansas City 10 days away, Dudar appears to have secured a starting job and will partner with Brandon McDonald or Dejan Jakovic in the heart of United’s back four.

“He’s a big guy, but he’s not slow and very athletic for his size. None of us [in the defensive corps last year] are tall, so he’s going to be important against bigger strikers,” said second-year defender Ethan White, who paired with Dudar in the second half of a 1-0 victory over the Chicago Fire here last Saturday in the Carolina Challenge Cup.

United will play the host team, the third-division Charleston Battery, on Wednesday and the Columbus Crew on Saturday.

Washington is Dudar’s 13th stop in six countries over a 13-year pro career. The Buenos Aires native ventured overseas for the first time in 2007 to sign with Swiss club Chiasso, went back to Argentina to play for Olimpo de Bahia Blanca, then returned to Switzerland for the next 3½ years. After a season with Bellinzona, Dudar transferred to Young Boys, where he was the league’s defender of the year in 2009-10.

Early in the following season, he scored in an UEFA Champions League qualifier against Fenerbahce of Turkey. Then on Sept. 12, in the eighth league match of the season, he and teammate Francois Affolter were attempting to nod the ball when their heads collided. For eight minutes, Dudar was treated on the field before being placed in an ambulance.

“It was a terrible sight,” opposing player Marco Streller said at the time on UEFA.com. “There was total silence in the dressing room at halftime.”

Doctors weren’t certain how severely Dudar was injured, so “they put me in a coma to check my brain and make sure I could function again.”

Stabilized, he was revived four days later. Upon waking, he was asked if he recognized his wife Lorena and a close friend. He did. It was then he asked to be taken to the stadium. Doctors had to explain to him what had happened.

For several weeks, Dudar underwent numerous tests and began to move around — slowly but without significant difficulty. “I had to train my brain again,” he said.

Two days after being released from the hospital, he rejoined his teammates for practice. “But not normally,” he said in a burst of English. “First month very hard.”

He wasn’t allowed to head the ball and would have to wear padded headgear.

“The doctor said it would be normal for me to be apprehensive, to have that fear, but as I played more games and had more training sessions, that fear went away,” he said through an interpreter. “I didn’t want to wear the pad on my head because I didn’t want to be reminded of the accident.”

As a precaution, he kept the headgear. And after missing 10 league matches, he regained his fitness during the Swiss league’s winter break and returned to the starting lineup Feb. 5, 2011, against Bellinzona.

Young Boys continued to monitor his health, subjecting him to periodic testing. Symptom free, he was allowed to shed the headgear. “I felt normal again,” he said.

At the start of the 2011-12 season, however, he fell out of favor with the coaching staff and dropped on the depth chart. Playing time was limited to reserve matches.

Relegated to the second unit, Dudar was eager to move and Young Boys was willing to let him go without a transfer fee. United initiated talks. The medical tests were the final hurdle to consummating a deal.

“I realize it was an incident I had to deal with and I’m thankful I was able to overcome it,” he said. “It’s in the past. I’ve moved on.”