Two people familiar with the case told The Associated Press that Pettitte was in Washington last week to meet with prosecutors. The people spoke on condition of anonymity because they were not authorized to discuss the ongoing investigation.
Pettitte could be a crucial witness for any case against Clemens. The two trained together for years. Pettitte has acknowledged taking human growth hormone and told congressional investigators that Clemens informed him nearly a decade ago that he used HGH.
Prosecutors are weighing whether to bring perjury charges against Clemens for denying under oath to Congress that he took performance-enhancing substances.
Lawyers for Pettitte did not immediately return calls seeking comment.
Much of what investigators wanted to know Pettitte had already told Congress.
Word of his recent involvement in the case came as Yankees superstar third baseman Alex Rodriguez answered questions at spring training camp in Florida about his own past use of performance enhancers.
Pettitte, who was at the Rodriguez press conference, was asked later about his meeting with prosecutors. "I can't talk to you about that," Pettitte said.
Around this time last year, Pettitte acknowledged that he might be questioned by the Justice Department.
"I'm just prepared that it might happen," Pettitte said at the time. "There's nothing I can do. Until somebody tells me to go somewhere, I can't do anything."
It was unclear whether Pettitte has been called before a grand jury. Because Pettitte has already given a sworn statement, prosecutors do not necessarily have to use the grand jury to make their case.
Personal trainer Brian McNamee has told federal agents, baseball investigator George Mitchell and a House committee that he injected Clemens more than a dozen times with steroids and human growth hormone from 1998-2001.
Clemens denied it, testifying that he did not use performance-enhancers.
"I have never taken steroids or HGH," the 354-game winner told a congressional committee a year ago.
Pettitte and another former Yankee, Chuck Knoblauch, both acknowledged to Congress that McNamee was correct when he said they used performance-enhancers.
The he-said, he-said nature of the sworn testimony given to Congress by McNamee and Clemens prompted lawmakers to ask the Justice Department to investigate whether the former pitcher lied.
The case was brought before a grand jury after an 11-month FBI investigation.
Clemens last pitched in the major leagues for the New York Yankees in 2007. Pettitte signed a one-year, $5.5 million contract to pitch for the Yankees this year.
Associated Press writers Matt Apuzzo in Washington and Ron Blum in Tampa contributed to this report.