The committee announced a new schedule Thursday of pre-hearing meetings with those witnesses.
Chuck Knoblauch, a former teammate of Clemens' with the New York Yankees, was subpoenaed to appear for a deposition or transcribed interview on Tuesday, although the committee said he has yet to be served.
Andy Pettitte, a longtime teammate and workout partner of Clemens', has been asked to appear Wednesday, with McNamee down for Feb. 7.
The fifth witness, former New York Mets clubhouse employee Kirk Radomski, originally was invited to meet with committee staff on Feb. 1, but his deposition or interview was given Thursday as "TBD" -- to be determined.
"The committee changed the dates to accommodate the schedules of the witnesses and lawyers involved," panel chairman Henry Waxman, a California Democrat, said in a statement relayed by a staff member.
Lawyers for Clemens and McNamee have said their clients will appear.
Joe Householder, a spokesman for Rusty Hardin, Clemens' primary lawyer, declined to comment any further, saying the pitcher's legal team would defer all comment on scheduling to the committee.
In the Mitchell Report on doping in baseball, McNamee said he injected Clemens with steroids and human growth hormone, accusations the pitcher with the eighth-most wins in major league history has denied repeatedly. Pettitte acknowledged McNamee injected him twice with HGH while the left-hander was recovering from an injury.
McNamee also told Mitchell he acquired HGH from Radomski for Knoblauch in 2001 and injected Knoblauch with HGH.
Radomski pleaded guilty to distributing steroids and laundering money. His sentencing is Feb. 8.
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