"They are a very, very good side," said Muller after the Sharks were outscored by five tries to nil at the venue for the forthcoming first Test between South Africa and the Lions.
"They have very good discipline and keep the ball through a lot of phases. They certainly build pressure that way.
"In the second half, if you have to defend for 80 per cent of the time, it is difficult and the wheels came off a bit for us at the end."
Muller, who has won 22 caps for the Boks and captained his country on their 2007 Tri Nations tour of Australasia, knows that the world champions will have to work hard for a series win.
The 29-year-old expects the Lions to provide the Boks with a competitive challenge, with Sharks head coach John Plumtree agreeing with Muller's assessment of Ian McGeechan's men.
"The Springboks will have to make sure they prepare smartly over the next 10 days.
"It's going to be a real dogfight out there, but the first Test will be really huge," added Muller.
"They aren't far off from being a pretty complete side," explained Plumtree, who also coached Wellington when they faced the Lions four years ago.
"This is a very different Lions team than the one that toured New Zealand in 2005 and there is no doubt in my mind that they are a couple of levels better than that squad.
"They took us on in the first-half and our boys took care of them, but they changed things in the second-half and we couldn't live with them.
"They are a strong squad with a lot of depth. I thought there were probably 10 to 11 Lions Test players on the park against us.
"They are building impressively, and the advantage they have over the Springboks is that you get the sense that they may be more advanced with the development of their structures than the Boks are at the moment.
"The Springboks are going to have to be very smart during their training camp over the next few days if they are going to beat the Lions."