Johannesburg - Beware Andrew Sheridan. The strong loosehead of the British and Irish Lions could be the spearhead of their attack on the Springboks come the first Test in Durban on June 20.

Three former greats in the front row have voiced their concerns about the South African scrum - and Lions coach Ian McGeechan, as astute as they come, will have noticed that Bok captain John Smit is uncomfortable at tighthead.

Former Springbok strongman tighthead Hempies du Toit, is impressed by Sheridan. Not only does the 117kg Englishman's power impress him, but Du Toit is also impressed with his technique. "I'm worried. John Smit has attributes as a captain, but it's so difficult to decide whether his captaincy makes up for moving him to tighthead," Du Toit said on Monday.

"Does he warrant the position of tighthead on form and ability? "Tighthead is unbelievably important, even today where the ball is put in skew into the scrums. Although one gets the impression that the front rows no longer bind as tightly as they did in years gone by - and that could lead to injuries - the tighthead position remains very important.

"On his own a tighthead cannot produce that right shoulder. That is a thing for the tight five as a whole.

"But if your tighthead is not up to it, it will allow the opposing scrum to get their right shoulder in.

"A tighthead must have lots of grunt, unpleasantness, and attitude. And he must not pop out, his shoulder must not be neutralised in the scrum," Du Toit said, and mused whether Smit's hand grip is strong enough for the position.

Du Toit is also wary of the role referees can play in the scrums. "They have no clue," he said bluntly, and added it could have a major influence on a match.

With the breakdown also a call that is more often than not at the whim of the referee, the 31st man on the field could well decide the series, said Du Toit.

Naka Drotske, Cheetahs coach and a man who was a member of the 1995 Springbok squad that won the World Cup, rates Sheridan very highly.

Sheridan is Drotske's choice to exploit the perceived weakness of the Springbok scrum at tighthead.

"Sheridan's scrummaging sets him apart," said Drotske to the planetrugby.com website.

"He's shown when he's good, he's really good. He can destroy any tighthead, which is why I said before the game he and Tony Woodcock, scrum-wise, are the best looseheads in the world.

"The Lions have a lot of depth, they always will. So it's hard to pick on any one player. But if I was a coach, I'd be picking him.

"If the Boks had a specialist tighthead such as Jannie du Plessis, you might look for different options, like Gethin Jenkins who gives you a better work-rate.

"There are not a lot of weaknesses in any international team, so if you see one, you have to break it.

"It's a big ask for John Smit to play tighthead in a game such as this. I am worried. I know if I was the Lions coach, that's where I would attack them," Drotske is quoted by the website.

Legendary tighthead Hannes Marias, who captained the Springboks against the invincible British Lions of 1974 and is also a former convener of the national selection committee, is just as critical of the selection of Smit as tighthead, although he reserved his opinion on Sheridan as he had not seen enough of him.

"John is obviously an outstanding captain, even irreplaceable.

He is an inspiration to his team and they believe in him.

"However, we cannot afford to go into the series with John at tighthead. He has battled or at least been uncomfortable every time he has played there for either the Springboks or the Sharks.

"(Springbok coach) Peter de Villiers, if he has decided he won't go with another captain, should've played John at hooker, where he is still one of the very best.

"If the coach feels otherwise, he should select another captain, not compromise with him at tighthead."

Wise words from a man who thinks before he speaks, and who is better qualified than most after 35 Tests of which 11 were as captain and 75 matches in all - including on the unbeaten tour of Australia in 1971 for South Africa - in this toughest position of all.