"I would say they are the most physical team I have played against, just in terms of the contact area, the rucks, the mauls, the tackles," Sheridan told Sky Sports.
"They are a very physical, aggressive bunch of players to come up against."
The former Bristol lock had only one England cap to his name when he made his Lions bow four years ago but he now knows exactly what to expect against the Boks.
Sheridan has faced the South Africans on three previous occasions with England, including the 2007 World Cup Final in Paris. On each occasion, the Bromley-born loose-head has finished on the losing side.
"The Lions have obviously tried to pick the strongest possible squad and throughout there are good players so hopefully we will be able to present a strong challenge to the South Africans," added Sheridan, who missed out on a Test appearance during his first Lions adventure.
"It is hard to know when you have got players coming from four different countries to see how they gel together and what sort of performances we can put in and particularly when you are against the world champions.
"I went on the tour four years ago and thoroughly enjoyed it then. But it's not always about experience, it is getting out there when you get your opportunity and trying to put 100 per cent into it.
"I'm absolutely delighted and really looking forward to it. It's the pinnacle."