Jim Mallinder backed referee JP Doyle's decision to only issue a yellow card to Leicester Tigers wing Adam Thompstone in Saints' defeat at Welford Road on Saturday evening.
Thompstone was involved in an incident with George North during the first half of the Aviva Premiership match, which Tigers won 19-11.
North went up to gather the ball and Thompstone was underneath the Saints wing, who crashed to the ground.
Doyle discussed the replays with television match official Trevor Fisher and concluded that a yellow card was the right course of action.
And Mallinder said: "I think the referee and the TMO got it right.
"It was unfortunate but I don't think he landed on his head or neck, he landed on his side and the head banged the ground.
"It was one of those things."
BT Sport pundit Ugo Monye was among a number of people watching the game to declare that Saints were wrong to keep North on, feeling the Wales star was concussed.
But Mallinder defended his club's medical staff, who made the decision, stressing they were sure the 24-year-old was fit enough to remain on the field.
"I don't make those decisions and what our doctors, medial staff are really, really clear about is that if anybody gets unconscious or had a knock where they look like they are concussed, then they need to come straight off. It's as simple as that," Mallinder said.
"You wouldn't go to be assessed, you'd be off straight away.
"George has had some previous issues so he took it steady.
"I haven't actually spoken to him, but the doctor was very, very happy, even as he walked off to go for an assessment.
"Thankfully he could come back on."
And Mallinder added: "It is our doctor who makes those decisions, but I also know there are more medical protocols that go on in terms of people looking at the incident.
"We actually have a trained medic here who also looks at that.
"He got up and it looked pretty nasty at the time. We've got to protect these lads.
"We're all for, if they're injured, getting them off, but thankfully George was happy to carry on, the medical team were happy that he wasn't concussed and he could carry on."
Saints were robbed of a losing bonus point late on as Owen Williams stuck the knife in with a last-gasp penalty.
Mike Haywood's try had got Mallinder's men back in the game after they went 10-0 down early on.
But Thompstone's score, allied with 11 points from Freddie Burns, put Tigers in control before Williams made the game safe late on.
And Mallinder said: "It was a mixed performance.
"There was a lot of effort, some good parts and again our set piece has been going well all season.
"Our defence was good and we held them out for long periods.
"We did have a few opportunities, which, when you're away from home, you need to take.
"We were in with a chance with a few minutes to go, but we got turned over on the line and ultimately giving away that penalty is very disappointing."