Injured Steyn remains doubtful while Morkel is back in South Africa after an injury in the first match against India in Cardiff on Thursday.
Speaking ahead of the crucial Group B match at Edgbaston, Misbah said they will surely have some advantage but they cannot afford to relax.
"Obviously, when main players of the opponent's team are missing, it will give you a psychological advantage. But at the same time, we are aware of the fact that they are a good team. They won a game against us when both of Steyn and Morkel weren't playing in South Africa. So, they are a quality side, and at the moment their strength is their batting. So we just can't relax," he said.
Both Pakistan and South Africa have lost their first group league games against West Indies and India, respectively. A win for either team is mandatory to keep hopes of a semifinal berth alive.
Misbah says Pakistan are used to such pressure situations.
"It's not a new story for us. In South Africa, we were in a similar situation like that in the ODI series, when we had to win the fourth ODI and our team did exceptionally well with that.In ICC tournaments, most of the time we are in similar situations," said Misbah.