The FAA's acting chief Daniel Elwell confirmed the organisation's technical experts will conduct a full and thorough review with "no stone unturned" as they assess Boeing's proposed solutions to fix an issue linked to two fatal crashes since October last year.
According to Bloomberg, he said: "If it takes a year to find everything we need to give us the confidence to lift the order, then so be it.
"If there is a crisis in confidence, we hope this will help to show the world that the world still talks together about aviation safety issues."
The MCAS flight control system has been blamed for two crashes in Indonesia and Ethiopia which killed 346 people, and Boeing recently revealed plans to schedule a certification flight with FAA crews to analyse the update.
The company's chairman, president and chief executive officer Dennis Muilenburg said: "We're committed to providing the FAA and global regulators all the information they need, and to getting it right.
"We're making clear and steady progress and are confident that the 737 MAX with updated MCAS software will be one of the safest airplanes ever to fly."
There remains no timeline for the 737 Max being able to carry passengers again, but a report from the Wall Street Journal has suggested the plane won't be back the skies until at least mid-August.