Pearce held a de-briefing day to talk to each of the City players individually, and although every other player managed to stick to the allotted times for their appointment, Barton turned up half-an-hour late.
Pearce was said to be livid with Barton, who still has an unsigned £28,000-a-week contract on the table.
Barton is entering the final year of his contract but there have still been no offers for his services.
This latest incident comes in the wake of Barton arriving late for physio treatment following a minor knee operation that kept him for a month towards the end of this season.