The two sides meet in the first leg tie at Cape Town Stadium on Saturday (15h00).
Sundowns played Wydad Casablanca in Morocco in the CAF Champions League last Friday. They landed on Sunday, before taking on Highlands Park in the Absa Premiership on Wednesday.
The players were given a day off on Thursday, before taking on the Citizens on Saturday.
City, meanwhile, played last weekend in a league match against Golden Arrows.
“Tomorrow we play a team that we don’t know when they last played. We foresee another challenge,” Mosimane said.
“You know that we have been on the road for some time. We went to Polokwane and came back. Within two days we did Arrows. Within two days we were travelling to Casablanca. Within two days of being back from Casablanca, we played Highlands Park. Within two days we have Cape Town City and after that we have the game of our lives against Horoya in the Champions League.
“If you ask me about preparations, it’s hectic. We knew about it and we can’t complain. It’s part of our lives. We are Sundowns and we want to compete in all the tournaments.”
He continued: “MTN8 is important for us, it’s important for the team to win it. As you guys say we have not won the MTN8 since I came to Sundowns.”