Arendse is suspended after receiving a fourth booking in the Brazilians' 1-0 win at Bloemfontein Celtic last night.
Mabunda and fellow midfielder Kekana, who are both one caution away from a one-match ban, featured against Phunya Sele Sele, with the former replacing Khama Billiat with 10 minutes to go at Dr Molemela Stadium.
Mosimane told SuperSport after the league tie: "We don't care who is on top, we aren't looking at the games in hand, we are looking at the next game. Orlando Pirates is the next game.
"Wayne Arendse is upset, he got a yellow. I dont know what, the referee said he was talking. We don't have him against Orlando Pirates, but look we got Thabo Nthethe, we got Bangaly [Soumahoro] who can come in and slot in there.
"Look, hectic, hectic progamme, that's why we rested Khama also, we took him out. That's why we kept Mabunda, he's also on a yellow and Kekana is on a yellow, so at least I must have one for Saturday. But I'm lucky now that Kekana didn't pick up a yellow, so I still have both of them. But as you say, hectic programme. We got experience of this, we regenerate the players, we rotate the players.
"One needs the three points. Sometimes we like to score five or four, but we just need the three points. So let's go step by step, one goal at a time and don't look at the top. Look at the process and the outcome will sort itself out."
Downs are fifth on the table with 22 points from 10 games - six points shy of leaders SuperSport United, but with five matches in hand.
Pirates are 10th in the standings with 19 points from 14 fixtures.