Lighthizer made the remarks at White House meeting of President Trump's Cabinet. Trump told Lighthizer he was in no rush for a resolution over the pact and to walk away from talks if need be.
"We’re either going to do a fair NAFTA for us or we're not going to do NAFTA at all," Trump said. "If you can’t make the right deal, don’t make it."
U.S. negotiations with Mexico are set to continue Thursday afternoon.
U.S-Mexico talks resumed in July, without Canada, after negotiations involving all three members of the $1.2 trillion trade bloc stalled in June.
Mexican officials on Wednesday said that Mexico and the United States may not meet their goal to finish talks by the end of August.
(Reporting by Steve Holland; Writing by Susan Heavey; Editing by Nick Zieminski)