Jim Mallinder came out in support of Dylan Hartley after the Saints skipper was sent off for swearing during the Premiership final.
Hartley, who had already been warned about his behaviour, was dismissed for allegedly saying ‘you f*****g cheat’ to official Wayne Barnes on the brink of half-time.
Barnes had awarded Leicester a scrum after Stephen Myler kicked the ball out without it bouncing as time was up at the end of the first 40 minutes.
Hartley then reacted verbally and became the first player to be dismissed in a Premiership showpiece as Saints fell to a 37-17 defeat to Leicester Tigers.
But Mallinder says Hartley told him he was aiming the insult as Tigers hooker and England team-mate Tom Youngs and refused to criticise his captain.
The Saints director of rugby said: “It’s very hard because you’re a long way from the field and you don’t know what’s going on, but I asked Dylan at half-time and I’ve asked him again, ‘what did he say’, and he said he was talking to Tom Youngs.
“If you talk like that to a player, you wouldn’t expect anything like that (the red card) to happen, but clearly Wayne Barnes believes he’s spoken to him.
“I support Dylan. He’s our captain and if he says he wasn’t speaking to the referee and he was speaking to a player on the floor I support my skipper in what he says.”
Saints were 16-5 down at the break and, despite the most spirited of showings during the second half, could not recover to claim victory.
Tigers scored three tries after the break to secure the Premiership crown and Mallinder admitted the sending off was the key moment.
“It was a massive turning point,” he said. “I read that Wayne Barnes didn’t want to be that person to make a decision, he wanted the rugby to determine who won the game and it was a massive decision that Wayne made.”