Hartley was red carded for a dangerous hit on Sean O'Brien during a Champions Cup game
Eddie O'Sullivan believes Dylan Hartley's chances of captaining the Lions on the 2017 tour to New Zealand will be severely impacted by his red card against Leinster.
Added to a record of 54 weeks worth of bans during his career, Hartley was red carded for a dangerous hit on Sean O'Brien during a European Champions Cup game between his Northampton and Leinster.
Another suspension is likely and his chances of leading the Lions is reduced.
"You can't have the red mist descending like that. I mean, that could cost you a Lions series," O'Sullivan said on Off The Ball.
"Guys get red carded in games where they make a bad judgement. They go and make a tackle, the guy ducks, it looks really bad and the referee says 'that's a high tackle, you're gone'."
But O'Sullivan drew a distinction between those type of incidents and the Hartley case.
"He blindsided Sean O'Brien. It was a pretty cheap shot by any metric. He went in to do it and he did it and it was like the guy lost the plot completely.
"Now, maybe he was frustrated that he wasn't starting the game or maybe he was frustrated with something else, maybe he didn't enjoy his lunch - I don't know. But what he did was unacceptable at a professional level.
"So this guy wants to captain the Lions. Certainly Warren Gatland's going [to say] 'Hold on a minute. This guy could lose the Lions series for you in a moment of madness'. We all thought he'd got himself sorted."
O'Sullivan concluded that,"I think there are definitely huge question marks over his head now, no matter what suspension he gets. It's his temperament that's the question mark."
Northampton Saints' Dylan Hartley dejected after being red carded ©INPHO/James Crombie
"As a Lions captain, I just don't know how you can take that punt on him".
Meanwhile, the weekend's action saw Leinster defeat Northampton by 27 points away from home, Munster tear Leicester apart 38-0, Ulster edge out Clermont in a thriller and Connacht perform well despite defeat at Wasps.
O'Sullivan highlighted the poor performances of the two English sides against Munster and Leinster.
"I'd just temper things a little bit with Munster and Leinster. I thought Leicester were appalling. They brought nothing," he said on Off The Ball.
"I thought on Friday night, Northampton were as bad or worse in some ways. They were at home and they just didn't show up at all."
The former Ireland head coach feels Ulster were probably the most impressive performers overall however because of the strengths of the opposition in comparison to Leicester and Northampton.
"The performance of the weekend for me was probably the Ulster performance. They played a Clermont team that came to play. They really went behind and stuck in," he said.
"I thought Ulster really played well despite losing their shape in the last 20 minutes."