Updated

NEW YORK (Reuters) - Pittsburgh Steelers quarterback Ben Roethlisberger was suspended for six games without pay on Wednesday and must undergo behavioral evaluation for violating the NFL's personal-conduct policy.

The 28-year-old Roethlisberger, who won Super Bowls with Pittsburgh in 2006 and 2009, was accused in March of sexually assaulting a 20-year-old female college student in a nightclub.

He was not charged with any crime but NFL Commissioner Roger Goodell had said Roethlisberger still had violated the league's personal-conduct policy.

"Your conduct raises sufficient concerns that I believe effective intervention now is the best step for your personal and professional welfare," Goodell said in a statement.

"In your six years in the NFL, you have first thrilled and now disappointed a great many people. I urge you to take full advantage of this opportunity to get your life and career back on track."

Roethlisberger cannot participate in any off-season team activities until after he has completed a professional behavioral evaluation by medical professionals.

Goodell said he will review Roethlisberger's progress prior to the start of the regular season and could reduce the suspension to four games but may also opt to extend it if Roethlisberger fails to co-operate with terms of the suspension.

If Roethlisberger serves the full six-game suspension, he will be eligible to return for Pittsburgh's game against the Super Bowl champion New Orleans Saints on October 31.

But if the suspension is reduced to four games, he will be eligible to return for Pittsburgh's game against division-rival Cleveland on October 17.

Roethlisberger went 9-6 last season as the team's starting quarterback with 26 touchdown passes and 12 interceptions but the Steelers fell short of the playoffs for the first time in three seasons.

The suspension came one day after the Steelers acquired quarterback Byron Leftwich from Tampa Bay in exchange for a seventh-round draft pick.

(Writing by Frank Pingue in Toronto; Editing by Justin Palmer)