The two Gauteng giants will clash in a massive Premier Soccer League (PSL) match on March 17 in what will be Sundowns' fourth game in 10 days.
On the other hand, Pirates will go into the game after a 10-day break having played their last match on March 7 which was a draw with Lamontville Golden Arrows.
Mosimane and his charges have been preparing for Saturday's Nedbank Cup quarter-final clash with Highlands Park having defeated Stellenbosch FC 1-0 in midweek.
“It’s very difficult for us because we are playing against well-rested teams. I heard the coach of Orlando Pirates talking about our game and I was surprised," Mosimane told the media.
“But what I forgot is that it is their next game but I still had Stellenbosch and Highlands before that. When I realised I said‚ ‘OK‚ they are going to be well-rested’.”
He also stated his charges were tired against Stellies despite having secured a win thanks to Themba Zwane's first-half goal.
“The two legs against Al Ahly and trying to fight back took a lot out of us. They gave us a scare but we know how to deal with stress and pressure‚” he continued.
Sundowns, who have a game in hand, are currently placed second on the league standings - four points behind leaders, Kaizer Chiefs.
Mosimane remains hopeful they can beat Chiefs to this season's league title and make it three successive PSL trophies.
“The league is decided in May. We need to keep our feet on the ground. We are holding onto the trophy and we don’t want to let it out of the cabinet," he added.
“We are still seeing it‚ we still love it so we cannot release it. So we are trying to protect it. But the game in hand doesn’t mean anything. We had two games in hand but at least we got rid of one.
“Only until you get rid of that game in hand‚ and you’ve won it‚ then you can start looking at the table differently.”