KANSAS CITY, Mo. -- Running back Larry Johnson issued his second apology in a 12-month span Tuesday and was told to stay away from the Chiefs while the NFL and the team complete their investigation into his use of a gay slur.

As Johnson released his apology, a national gay rights advocacy organization called on the league and the team to take disciplinary action against the two-time Pro Bowler.

The latest chapter in Johnson's stormy career began Sunday night when he questioned first-year Chiefs coach Todd Haley's football credentials via Twitter.

Johnson used the slur during an exchange with one of his Twitter followers. One day later, he used it again as he brushed off reporters and told them he wouldn't comment, according to the Kansas City Star, which recorded the comment.

Haley refused to address the matter Tuesday, saying it was still being investigated.

"I'm just not going to comment any further because there is some stuff going on," Haley said.

Johnson, who turns 30 next month, signed a five-year contract extension in 2007, and the deal included $19 million guaranteed and could be worth up to $45 million. The Chiefs could be checking to see whether Johnson violated contract provisions that would allow the team to cut him with reduced financial obligation.

Last spring, an arbitrator ruled that the Chiefs could release the running back and not owe him $3.5 million in guaranteed money because he had violated contract conditions by pleading guilty to disturbing the peace in another incident. But the issue became moot when the team elected not to cut Johnson, and until he began tweeting Sunday night, the often-volatile running back had been on good behavior.

The Chiefs said they have told Johnson that he wouldn't be allowed to practice with the team or participate in team activities until the matter is resolved, though he hasn't been suspended. NFL spokesman Greg Aiello said the league would have no comment pending the investigation.

Johnson, who needs just 75 rushing yards to become the Chiefs' all-time leader, apologized to Haley, the team, fans and the league "for the words I used."

"I regret my actions. The words were used by me in frustration, and they were not appropriate," Johnson said through a spokesman. "I did not intend to offend anyone, but that is no excuse for what I said."

The apology sounded similar to one that Johnson made almost exactly one year ago after one woman accused him of throwing a drink on her and another said he had pushed her. The incidents happened separately in Kansas City nightclubs and led to Johnson being sentenced to two years' probation after pleading guilty to two counts of disturbing the peace.

"I'm going to work to that point to get my life back on track and know that I and I alone put myself in these critical situations and environments to where things don't come out favorably to me," Johnson said on Oct. 22, 2008.

At the time, Johnson was benched for three games by then-Chiefs coach Herm Edwards and suspended for one game by NFL Commissioner Roger Goodell.

On Tuesday, Johnson apologized to "all the kids who view athletes as role models. I was not a good role model yesterday, and hopefully I can become a better role model. We all make mistakes, and the challenge is to learn from them.

"I will do my best to learn from this one as I move toward becoming a better person, teammate, and member of the Kansas City Chiefs team and community."

Johnson's agent said all his client could do now was wait.

"It's up to the NFL to investigate it and see what they want to do, and we will respond accordingly," Peter Schaffer told The Associated Press. "We've apologized. Larry's trying to move forward. It is what it is right now."

Jarrett Barrios, president of the Gay and Lesbian Alliance Against Defamation, called on the NFL and the Chiefs to take disciplinary action and seize a chance to educate "on the dangers of homophobia in sports."

Such slurs are used to "ridicule and harass young gay and transgender athletes on local sports fields across America," Barrios said.

Barrios said he welcomed the apology.

"Larry Johnson's apology sends an important message that there is no excuse for using anti-gay epithets," Barrios said.

Drafted in the first round out of Penn State in 2003, Johnson was one of the best running backs in the NFL in 2005 and '06, rushing for more than 1,700 yards in each season. This season, like the Chiefs, Johnson has struggled, averaging just 2.7 yards per carry.

Kansas City (1-6) is on its bye week.