Northampton Saints director of rugby Chris Boyd faces a disciplinary hearing for criticising the performance of referee Adam Leal in his team’s loss to Saracens earlier this month.

Boyd said Leal “didn’t have enough nuts, did he?” after failing to issue a yellow card against Mark McCall’s team during a series of scrums under the posts at a stage when the match was evenly poised.

Even though Saints had been awarded successive penalties at the set piece and Saracens had been warned, Leal opted to give the next infringement against the hosts, who went on to lose 30-6 on 2 January.

“He didn’t have enough nuts, did he? I mean it was a clear hinge. There was only one side under pressure in that series of scrums,” Boyd said.

Boyd will appear before a virtual independent disciplinary hearing on Thursday evening for conduct prejudicial to the interests of the union and the game, contrary to Rugby Football Union rule 5.12.

Although no sanction table exists for the charge, a wide range of punishments – including fines and match-day bans – are available to the three-strong judiciary panel.

Boyd is expected to leave Northampton at the end of the season after choosing to return to his native New Zealand rather than activate the optional year on his contract.