Mark Boucher described losing Kagiso Rabada for the final Test against England as a "massive blow" and had mixed feelings over the suspension handed down to the South Africa quick.
Rabada will miss the last match of the series at The Wanderers after being sanctioned for his reaction to dismissing Joe Root on day one of the third Test at St George's Park.
The paceman roared in celebration after bowling the England captain and that resulted in him being found guilty of a level one breach of the ICC code of conduct.
It earned Rabada a fourth demerit point in a two-year period, a tally that triggers a one-match ban.
Boucher felt Rabada should have known better, but suggested the punishment was harsh after watching England take charge in Port Elizabeth by posting 499-9 declared before the Proteas were reduced to 60-2 in reply on Friday.
"I think KG has a bit of a history, he probably shouldn't have done it, but it is what it is," said the South Africa head coach.
"The level one is a slap on the wrists but unfortunately he's got too many demerit points. We played in days when bowlers used to swear at batsmen, you want to be nice and aggressive.
"He didn't look at Joe Root, but it's about how you determine the laws. KG is best when he's nice and aggressive. We'll get him to run to square leg rather than the batter. But the laws are there and you have to abide by them.
"I wasn't aware of all the demerit points [Rabada has] and how the whole system works, so to hear this morning he's going to be banned for the final Test is a massive blow for us.
"He's a world-class performer, especially at The Wanderers, where I think he would be very effective."
The former South Africa wicketkeeper-batsman added: "We spoke to the match referee [on Thursday] and we did voice our concerns over the rule and a couple of variations of the rule.
"It's a tough one to gauge about excessive celebrations in the area of the batter and making contact with the batter.
"I don't feel that he made any contact with the batter whatsoever. Yes, he was in his space, but the two put together there is probably different ways you can look at it. Bottom line is the match referee has made up his mind."