The area from Oxford Circus to Portman Street was shut to traffic for eight hours on Saturday and Sunday.
Westminster City Council said similar closures could happen on future weekends unless the site can be redesigned.
Westminster City Council transport commissioner Martin Low said: “This was a pre-emptive decision in response to concerns about possible crushing on the pavements as a result of narrower walkways, which are being caused by ongoing construction works.
“The council is hopeful that a redesign of the building site will be possible going forward, but cannot rule out further weekend traffic closures at this stage.
“Our paramount concern is to ensure the safety of pedestrians during this busy weekend of Christmas shopping in Oxford Street.”