Will Greenwood says Owen Farrell "knows he's crossed a line" after getting a five-match ban for his tackle on Wasps' Charlie Atkinson.
The England captain was shown a straight red card for his swinging-arm hit on the 18-year-old, and on Tuesday was handed a 10-match ban that was reduced to five games for "off-field mitigating factors" that included testimonials from England coach Eddie Jones and Saracens boss Mark McCall.
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Greenwood says Farrell's tackling technique is a "work in progress" and that the hard-hitting fly-half presents a conundrum when it comes to curtailing the way he naturally plays the game.
Greenwood told Sky Sports News: "It's a bit like the old Wayne Rooney argument: do you take the mongrel out of him and try and get him tackling in a more sanitised fashion? Does that remove how he plays?
"He's not daft, Owen knows he's crossed a line here. He knows he tackles high, they've got to just keep working at it.
"He has shown remorse. Could it come back and hurt England in a key moment? Absolutely. Is he blind to the fact that he tackles high? No. Work in progress."
Greenwood is in favour of rugby's authorities clamping down on reckless tackling, and says players are more aware than ever of their defensive responsibilities.
"I'm a huge fan of what the referees are doing," Greenwood said.
"Head injuries and head-injury assessments are being watched very carefully and monitored by referees. Any injury to the head; physios and independent doctor reviews are being done in tunnels and in changing rooms to make sure they can't re-enter the field if injured.
"Anything coming in at the nipple line is an immediate foul, a transgression, a penalty, and more often than not a pretty straight yellow card.
"Anything that's swinging and reckless and contact with the head is a straight red.
"Owen Farrell was absolutely aware the second he made contact with young Charlie Atkinson against Wasps at the weekend it was a straight red. He almost walked before the red was brandished."
Farrell ban the latest bitter blow for Saracens
Sky Sports News' James Cole:
Owen Farrell's five-game ban may be good news for England but it is terrible news for Saracens.
The Premiership champions have endured an 'annus horribilis' - and it shows no sign of ending. Farrell will be unavailable for their Champions Cup quarter-final against Leinster; their last chance of silverware before they're relegated to the Championship for breaching the salary cap.
Alex Goode or Manu Vunipola will start at 10 on September 19. The Irish province will now be firm favourites.
There is however another issue in play here - Farrell's tackle-technique.
The red card he received last weekend has been threatening for some time. He often aims high and with a swinging arm, trying to dislodge the ball from his opponent. Often it is brilliant. But sometimes it is reckless.
With World Rugby looking to eradicate high tackles, Farrell is leaving himself liable to split-second misjudgements and disciplinary-hearing judgements. Perhaps England coach Eddie Jones will look to address this sooner rather than later.