The county council plans to prohibit buses, taxis and private hire vehicles from using Queen Street.
Oxford Bus Company said the authority needed to consider the "additional pressure" on surrounding streets.
The council said it was "vital" for more pedestrians and cyclists to use the route.
Oxford bus Company said: "We can't have a situation where Queen Street is pedestrianised but the additional pressure put on surrounding streets means that waiting conditions for bus passengers become unbearable, or walks between stops become unacceptably long - or our customers can't get taken to where they want to go.
"A credible, agreed plan therefore needs to be identified between all parties before Queen Street can be closed and dialogue is ongoing to achieve this."
Oxfordshire County Council said the street was one of the main routes across the city centre and added pedestrian and cycle numbers were expected to increase "significantly" in the future due to development across the city.
"It is vital that strong pedestrian and cycle links are maintained and encouraged, and improvements to the pedestrian experience are made, to ensure a well-connected and joined up city centre that will continue to thrive," it added.
A consultation on the proposals runs until 6 June.
A "credible plan" needs to be agreed before any move to ban buses and taxis from a street in Oxford is made, a bus company has said.