The reigning PSL champions are second on the log with 32 points in 16 matches, while log leaders Kaizer Chiefs are on 41 points in 17 matches.
Pirates are in the sixth position with 24 points in 16 matches. Mosimane is expecting a very difficult match.
Meanwhile, Sundowns reached the quarter-finals of the CAF Champions League when they beat USM Algers from Algeria 2-1 in Pretoria on Saturday.
Sundowns are in top of Group C with 10 points in four matches, followed by Wydad Casablanca on six points with the same number of matches.
USM are third with two points and Petro de Luanda is rock bottom also on two points. The Brazilians have not lost at home in the last 18 Champions League matches.
Sundowns are bidding to win the champions league, the PSL title and the Nedbank Cup. With the champions league qualification sealed, Sundowns will now focus on the league and the Nedbank Cup according to Mosimane.
After Pirates, Sundowns will proceed to meet SuperSport United in another league match on Sunday.
They will then meet Petro de Luanda on the 25th of this month in the Champions League and on the 31st they will host Wydad. Mosimane says their schedule is still very tight.
Sundowns missed key strikers Mauricio Affonso, Ali Meza, Phakamani Mahlambi, Anthony Laffor and Siphelele Mkhulise against the Algerians.
They missed so many opportunities to seal the match. USM could have gotten a late equalizer but Mohamed Meftah rattled the crossbar. Mosimane will be looking to sign another striker. – Report by Vincent Sitsula