Tyler Hamilton.

THE ASSOCIATED PRESS

NEW YORK -- Former professional cyclist Tyler Hamilton has been subpoenaed to appear before a grand jury, though his lawyer refused to say whether it has anything to do with a federal investigation involving former teammate Lance Armstrong.

Chris Manderson said late Friday that Hamilton, a teammate of Armstrong on the U.S. Postal Service team, "understands his legal obligations" and will co-operate with the grand jury.

The subpoena of Hamilton was first reported by ESPN.com.

"I can't comment on whether it's the Lance Armstrong doping case," Manderson told The Associated Press. "I can't comment on anything other than the fact that it's been received and he will co-operate."

Hamilton is among several former teammates and staff members of Armstrong to have been contacted by investigators since disgraced cyclist Floyd Landis went public with allegations of organized doping on the U.S. Postal Service team. Armstrong was the leader of the team, which later become Discovery Channel, and helped him win a record seven Tour de France titles.

Armstrong has continually denied doping allegations, and recently hired former federal prosecutor Bryan D. Daly to represent him in the face of possible fraud and doping violations.

The cancer survivor returned from a brief retirement to finish third in the Tour last year, and is 23rd in the overall standings with two stages left in this year's race. The team that Armstrong helped organize, Team Radioshack, leads the team standings.

The questions about doping have followed Armstrong throughout this year's race, which he has already announced will be his final Tour de France. Armstrong said that he wants to devote more time to his family and the Livestrong Foundation.

Landis served as a support rider for Armstrong from 2002-04, before leaving for Swiss team Phonak and winning the 2006 Tour. He was later stripped of his title for doping and fought the charges until May, when he finally admitted to using performance-enhancing drugs throughout his career and implicated Armstrong in organized doping.

Three-time Tour de France champion Greg LeMond, a fierce critic of Armstrong, also has reportedly been served with a grand jury subpoena as part of the investigation.

Hamilton was never on the same team with Landis, riding with the U.S. Postal Service team in support of Armstrong until 2001. He won the 2004 Olympic gold medal in the time trial in Athens, but failed a test for blood doping afterward and eventually served a two-year suspension.

Hamilton returned to racing and won the 2008 U.S. road championship, but retired last spring after admitting that he took an antidepressant that contained the banned steroid DHEA. He was officially banned from cycling for eight years, and has since founded Tyler Hamilton Training, a company that helps coach all levels of cyclists.

"He really didn't want to be involved in this, but when the federal government comes calling, you have to answer," said Manderson, who has also represented Hamilton in the past. "He would rather focus on his battle with depression and his training business."