Bryan Namoff, a long-serving D.C. United defender whose career was cut short by a concussion three years ago, filed a $12 million lawsuit Wednesday against the MLS club and former coach Tom Soehn, claiming they failed to properly evaluate his injury and cleared him to play too soon.

The complaint, filed in D.C. Superior Court, alleges United was “negligent in its management, care and treatment” of Namoff after he was injured in a game at RFK Stadium on Sept. 9, 2009. He played three days later, which ultimately was the final appearance of his nine-year career.

Namoff, now 33, says he suffered brain damage and cognitive, memory and sensory loss. He also has permanent headaches and fatigue, sleep problems and hypersensitivity to motion, the lawsuit says.

Namoff’s wife Nadine is a co-plaintiff. They are seeking $10 million for medical negligence and $2 million for the impact on their marriage. Namoff has not been able to work in two years and has continued to incur medical expenses.

United spokesman Doug Hicks said the club wouldn’t comment on pending litigation.

Namoff’s attorneys plan to add United athletic trainer Brian Goodstein, former team physician Christopher Annunziata and Commonwealth Orthopaedics – Annunziata’s practice -- to the lawsuit in 90 days, per D.C. law regarding litigation involved health car providers.

Namoff’s case is the latest pertaining to concussions suffered by pro athletes.

More than 3,000 former NFL players have filed suit against the league, claiming it concealed long-term effects of head trauma for decades. In 2000, Merril Hoge received a $1.55 million jury verdict in a lawsuit against a former Chicago Bears physician. He had alleged that mistreatment of a concussion led to more serious injury.

This year, Clay Rush, a former player in the Arena Football League, reached an undisclosed settlement with a Denver hospital chain that employed a doctor whom, according to the lawsuit, improperly cleared Rush to play despite two concussions in 15 days.

Several MLS players have retired prematurely because of concussions, including three of Namoff’s former teammates: Alecko Eskandarian, Josh Gros and Devon McTavish.

Namoff has said he suffered one concussion in high school and one in college at Bradley University but none in the MLS until the 2009 incident.

In 2011, recognizing the increase in severe head injuries, MLS implemented guidelines to educate, diagnose and treat concussions.

Steve Shapiro represented the AFL player and is working on the Namoff case with Washington-based Joseph Cammarata, who authored the Athletic Concussion Protection Act, a 2011 law that set guidelines for athletes age 18 and under in the District of Columbia who suffer head injuries.

Namoff had the third-longest tenure in club history behind Jaime Moreno and Ben Olsen (United’s current head coach) and is third in regular season games played and fourth in starts.

In 2009, he had played all but 14 of 2,340 minutes before being sidelined. In a late-season game against Kansas City, Namoff extended himself to head the ball when an opponent ran into him at full force with his shoulder, colliding with Namoff’s head to create a whiplash sensation.

Namoff wasn’t treated and remained in the game. Afterward, the complaint says, Namoff had vision problems, prompting Goodstein to request Annunziata and an optometrist. Proper treatment wasn’t given, the lawsuit claims, and Goodstein told Nadine Namoff that her husband had suffered a concussion.

In the three days between matches, Namoff “was not assessed, evaluated or examined” by United officials and didn’t practice but was allowed to play in the next game, the complaint says.

In the Seattle match, according to the lawsuit, Namoff “experienced and exhibited post-concussive symptoms, which were significantly exacerbated by the end of the game.”

Afterward, Namoff complained to Goodstein and Annunziata about trouble focusing and dizziness. The medical staff “merely stated that they would monitor him,” the suit says.

Annunziata, who worked with United between 2001 and 2010, is the Washington Redskins’ head orthopedic physician.

Soehn, who is now the Vancouver Whitecaps’ director of soccer operations, failed to act in Namoff’s best interests by permitting him to play three days after a concussion, the suit says. Reached by e-mail, Soehn said he didn’t want to comment.

Over the next several months, Namoff experienced migraines, nausea, dizziness and vertigo. The whiplash caused upper cervical trauma, affecting the joints and ligament in his vertebrae. Numerous specialists examined him, including Robert Cantu, the renowned neurologist and concussion expert.

In spring 2010, as United prepared for the upcoming season, Namoff was hopeful of playing again. He was doing light exercise and ball work. At the time, he said, “It’s nice to finally make some strides.”

The symptoms persisted, however. In July 2010, he suspended his career and joined the front office as a special projects manager. At the next home game, United supporters raised “#26” signs – his uniform number – and a thank you banner. Headaches, however, prevented Namoff from continuing to work for the club.

This spring, he volunteered to speak at a concussion-prevention meeting with students and parents at Washington-Lee High School in Arlington. “I am living with a brain injury. Don’t be like me,” he told them. At the first warning sign, he implored to parents, make an appointment with a neurologist.

Shortly after speaking, he had to step out of the auditorium because of sensitivity to fluorescent light – a common problem for concussion victims.

Later, he told a reporter, “Every minute of every day, I have a headache. It’s the invisible nightmare.”