Lamour's dismissal was confirmed on Monday (Tuesday AEST) in the latest domino effect of Infantino's proposal to sell stakes in a company to run the World Cup to private investors.
The plan by the Swiss supremo was rejected by three continental confederations before it was withdrawn and led to UEFA's threat to boycott all FIFA competitions.
During the infancy of the crisis, Lamour told the Associated Press that FIFA's administration had been "deceived" by Infantino, who remains under extreme pressure after three confederation presidents accused him of "deception" in an open letter published last week.
"FIFA can confirm that the working relationship between FIFA and Kevin Lamour as FIFA's Chief Operating Officer has ended on 17 August 2026," a spokesperson said.
"FIFA thanks Kevin for his two years of service and wishes him the best of luck for the future.
"No further comment will be made on the matter."
The Press Association understands staff were told in an email by FIFA secretary general Mattias Grafstrom of Lamour's departure before his work and role in improving relations with a number of stakeholders in the game was praised.
Lamour's exit occurred on the same day Infantino lost the support of the Scottish Football Association.
"The Scottish FA will not be voting for Gianni Infantino. That's in line with the UEFA position and we've maintained that stance throughout," the governing body's chief executive Ian Maxwell said.
"When you're an administrator in football, you shouldn't be anywhere near the camera anywhere near as often as has been the case.
"Something has gone wrong if the focus after the most successful, the most well-supported World Cup, that every Scotland fan who was there will be talking about for the rest of their lives, has now become off-the-field incidents rather than on the field.
"That can't be where football should be. It's got to be focused on the game itself and on the relationship with the fans.
"The transparency and the governance needs to change."
Pressure on Infantino continues to mount but if he refuses to resign, one option for his opponents could be to find a candidate willing to stand against him in next year's Congress.
However, advocacy group FairSquare is calling for a different approach and has written to FIFA questioning Infantino's right to even stand for re-election.
FairSquare was supported in its letter by Miguel Maduro, the former chair of FIFA's governance committee.
The letter has been sent to FIFA's review committee, which is a sub-committee of the GACC and is empowered to make decisions on the eligibility of presidential candidates.
