The Commission's inquiry team said in its Emerging Thinking it did not agree with the calculation.
But this week Sainsbury's said: "The Commission and Sainsbury's use different assumptions relating to market definition and like-for-like growth. A misleading impression has been created by the Commission making direct comparisons and judgements about our projections."
The Commission told The Grocer the row had little bearing on its investigation. "We've said we're interested in the market on a local level, which means national market share is not forming part of our deliberations," a spokesman said.