Clemens filed the suit Sunday night in Harris County District Court in Texas, listing 15 alleged statements McNamee made to the baseball drug investigator George Mitchell. Clemens claimed the statement were "untrue and defamatory."
"According to McNamee, he originally made his allegations to federal authorities after being threatened with criminal prosecution if he didn't implicate Clemens," according to the 14-page petition, obtained early Monday by The Associated Press.
The suit, first reported by the Houston Chronicle, states that when McNamee told others that when he first was interviewed by federal law enforcement last June, he denied Clemens had used steroids or human growth hormone. The suit quotes McNamee as saying he was pressured by Assistant U.S. Attorney Matthew Parrella and IRS Special Agent Jeff Novitzky -- key members of the BALCO prosecution -- to implicate Clemens. The suit did not attribute where the quote from McNamee was obtained.
"After this exchange, and for the first time in his life, McNamee stated that he had injected Clemens with steroids in 1998, 2000 and 2001," the suit said. "Following his recantation, McNamee has relayed that he magically went from a `target' in a federal criminal drug investigation to a mere `witness,' so long as he continued to `toe the line."'
The suit said that when McNamee initially refused a request from federal authorities that he speak to Mitchell, he was threatened with prosecution. Clemens said McNamee decided only then to cooperate with Mitchell and the suit said McNamee told other the interview "was conducted like a Cold War-era interrogation in which a federal agent merely read to the Mitchell investigators McNamee's previously obtained statement and then asked McNamee to confirm what he previously stated."
Clemens asked that damages be determined by a jury.
"Clemens' good reputation has been severely injured," the suit said. "McNamee's false allegations have also caused Clemens to suffer mental anguish, shame, public humiliation and embarrassment."
McNamee's lawyers are likely to remove the case to U.S. District Court in Houston, since Clemens and McNamee reside in different states. McNamee also could ask that the suit be moved to federal court in New York.
The seven-time Cy Young Award winner, who was scheduled to hold a late afternoon news conference Monday in Houston, sounded indignant and defiant in a segment of CBS's "60 Minutes" broadcast Sunday night, his first interview since McNamee accused him. The pair are approaching a potential confrontation if the pair testify under oath at a Jan. 16 hearing on Capitol Hill.
The most prominent player implicated in last month's Mitchell Report, Clemens steadfastly maintained his innocence and called McNamee's allegations "totally false."
"If he's doing that to me, I should have a third ear coming out of my forehead. I should be pulling tractors with my teeth," said Clemens, who wore a lavender button-down shirt during the interview, taped Dec. 28 at his home in Katy, Texas.
On Friday, when the House Committee on Oversight and Government Reform invited Clemens and McNamee to testify, the pair spoke by telephone, an individual close to the situation said, speaking on condition of anonymity because public comments weren't authorized. The conversation first was reported Sunday by Newsday.
The individual would not say what was discussed.
Clemens' lawyer, Rusty Hardin, told the Chronicle that it was McNamee who arranged to talk to Clemens on Friday but instead of getting back to Clemens the conversation was leaked "with spin" to Newsday.
"We kept thinking McNamee might change his mind and come to his senses and admit he was lying," Hardin told the Chronicle.
McNamee also had been contemplating a suit.
"We welcome a lawsuit. It makes our decision easy," Richard Emery, one of McNamee's lawyers, said earlier Sunday. "If he sued McNamee, it would make things very simple."
During the "60 Minutes" segment, Clemens said he might be willing to take a lie-detector test and was "shocked" close friend Andy Pettitte used HGH. He said -- again -- that he probably will retire.
A fiery look in his eyes and stubble on his face, Clemens told CBS's Mike Wallace that he would have spoken with baseball drug investigator George Mitchell had he been aware of McNamee's accusations.
"I thought it was an impassioned, disingenuous and desperate plea," said Earl Ward, McNamee's primary lawyer.
One of the few revelations in the much-hyped interview came when Clemens was asked whether he conceivably would take a lie detector test.
"Yeah," he answered. "I don't know if they're good or bad."
After Monday's news conference will come the congressional hearing. Pettitte, former Yankees teammate Chuck Knoblauch and former Mets clubhouse attendant Kirk Radomski, who allegedly supplied McNamee with performance-enhancing drugs, also were asked to appear before the committee.
Lawyers for Clemens and McNamee have said their clients are willing to testify but Hardin wouldn't commit to the date.
Emery said he wanted to hear testimony from Clemens.
"If Congress calls him, he pretty much has to take the Fifth, and if he takes the Fifth, nobody will ever believe him again and all this effort has gone down the drain," Emery said. "And if he doesn't take the Fifth, it's very hard to imagine that a prosecutor isn't going to pursue this. So I think he's put himself in a terrible corner."
Clemens said his lawyer advised him not to speak with Mitchell, who spent 20 months on his investigation.
"If I would've known what this man, what Brian McNamee (had) said in this report, I would have been down there in a heartbeat to take care of it," Clemens said.
Only two active players, Jason Giambi and Frank Thomas, spoke with Mitchell, a Boston Red Sox director and a former Senate majority leader.
In excerpts of the CBS interview that were released Thursday, Clemens said McNamee injected him with vitamin B-12 and the painkiller lidocaine. In the full 14-minute broadcast, Clemens also said he was given an injection of toradol under the supervision of the New York Yankees.
McNamee told Mitchell he injected Clemens with steroids and HGH about 16 to 21 times during 1998, 2000 and 2001 -- before baseball players and owners agreed to ban performance-enhancing substances.
Eighth on the career list with 354 wins, the 45-year-old Clemens said he was angered McNamee's accusations have been accepted as truth by some.
"It's hogwash for people to even assume this," Clemens said. "Twenty-four, 25 years, Mike. You'd think I'd get an inch of respect. An inch."
Clemens said the descriptions McNamee gave Mitchell of injections "never happened."
"If I have these needles and these steroids and all these drugs, where did I get 'em?" he said. "Where is the person out there (who) gave 'em to me? Please, please come forward."