Wales's Kiwi coach Gatland is in charge of the Lions' forwards
The Lions are hoping to take advantage of South Africa's lack of recent game time when they clash in the first Test on 20 June.
While the Lions will have had six games together the Springboks have had just one warm-up match against Namibia.
The Lions are so far unbeaten in their opening four matches on tour.
"What we are counting on going into that first Test is that maybe they will be a bit underdone," said Lions forwards coach Warren Gatland.
"And that is traditionally what happens on tours like this.
"The touring side has a couple of games under their belt and the home side is a little bit rusty and underdone for the first Test and that's your big opportunity to catch them a bit cold.
"Some of their players haven't played for four or five weeks. Even if you have been in the gym and training pretty hard you still need games under your belt," Gatland said.
But Springboks captain John Smit says experience gained over the past five years will compensate for a lack of match practice, which has been restricted to a match against a Namibian Invitation XV on 29 May.
"I don't think we are short of rugby and the core of this team has been together for a long time and we've built some great combinations in that time," said Smit.
"I guess there are two trains of thought - you either play too much rugby and everyone says you're fatigued or you don't play and everyone says you're short of preparation."
The Lions meet South Africa in the first of three Tests in Durban before they clash again in Pretoria (27 June) and Johannesburg (4 July).
But while the Lions have won all four of their opening matches Gatland bemoaned the fact they have not faced quality provincial sides as South Africa have removed their international players from the warm-up games.
"It's always nice to play against the best players because you want the hardest possible preparation but we haven't had that opportunity," Gatland added.
"Likewise, some of them (the Springboks) would have benefited from being part of the warm-up games. They will have been hampered by not having faced us."
We have got to be able to compete, take South Africa through phases and everyone will have to empty the tank
The Lions carried on their unbeaten run by demolishing the Sharks by 39-3 in Durban on Wednesday and Gatland is pleased with the way his team have been performing.
"We have got to be prepared to go the full 80 minutes against South Africa. If we get into a slow, set-piece game and we let them dominate us with their potential power game we are going to struggle," he said.
"We have got to be able to compete, take South Africa through phases and everyone will have to empty the tank. The players are doing that at the moment and we can't ask any more of them."
The Lions' next tour match is against Western Province in Cape Town on Saturday.
Coach Ian McGeechan is expected to unveil his first Test line-up on Wednesday, 17 June.