Mahamutsa remains sidelined with an Achilles tendon injury that will keep him out for the rest of the season, and De Sa is not shy to reveal how much of a loss the 31-year-old has been.
"He has been a huge loss for me because I felt he was one of our best defenders," De Sa says.
"I didn't know him well enough until I joined Pirates, but having worked with him I realised what a fantastic player he is; so much so that when I spoke to Gordon Igesund I said if you are going to choose a defender from Pirates, Rooi is the one.
"He has been a really huge loss for us," says De Sa, who has seen his team leaking goals in recent weeks in the absence of another centre-back Siyabonga Sangweni, who made his return this past weekend.
De Sa also speaks positively about how useful veteran defender Lucky Lekgwathi has been as he approaches his 37th birthday.
"Lucky has been outstanding for someone his age, playing midweek, weekends and then go to Africa. He is unbelievable in the way he has been going and is still not finished. He will still play on and so we got to give him credit for that."