updated 7:53 p.m. ET April 20, 2007

YONKERS, N.Y. - Boston Celtics guard Sebastian Telfair was arrested early Friday after police stopped him for speeding and found a loaded handgun under a seat in his SUV.

Telfair, 21, of Brooklyn was stopped at about 4 a.m. on the Bronx River Parkway in Yonkers, N.Y. after being clocked at 77 mph in a 45-mph zone in his Range Rover, Westchester County police spokesman Kieran O’Leary said.

Neither Telfair nor passenger Al Eden Fuentes had a valid driver’s license, so Telfair’s SUV was set for impoundment and searched by an officer, O’Leary said. The officer quickly noticed the butt of the handgun sticking out from under the passenger seat, O’Leary added.

Telfair and Queens resident Fuentes, 28, said they knew nothing about the gun, O’Leary said. Police still were investigating whether the gun was registered.

Telfair and Fuentes pleaded not guilty Friday at Yonkers City Court to charges including felony second-degree possession of a weapon, and bail was set at $7,500. The pair was due back in court May 17.

“The players on the Celtics have been explicitly warned, this year, to obey the team and league gun prohibition as well as state laws. We take this very seriously, and will act accordingly once the facts have been determined,” owner Wyc Grousbeck said Friday night.

“We began the building process towards next year yesterday, and the last thing we want or will tolerate is a distraction along the way.”

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Celtics director of basketball operations Danny Ainge declined to comment.

O’Leary said Telfair was polite and cooperative.

“Our officers said he behaved like a gentlemen,” O’Leary said.

A clerk at the Yonkers court did not have the name of Telfair’s attorney, and it could not be immediately determined who was representing him.

Telfair, the 13th pick in the 2004 NBA draft, was traded to the Celtics last year from Portland.

While Telfair was with Portland in February 2006, he was questioned after a handgun registered to his girlfriend was found in his pillowcase aboard the team’s plane at Logan International Airport in Boston. The Trail Blazers later fined Telfair and suspended him for two days.

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