Mwila joined the South African club from Green Buffaloes this week on a three -year deal.
This means Mwila is now ineligible for CHAN duty.
CHAN is a second tier AFCON for domestic-based players first staged by CAF in 2009.
“Brian has been a very important player in our team. I think his absence has clearly been felt,”Nyirenda said.
Mwila scored five goals in seven games for Zambia since making his Chipolopolo debut in a 0-0 away draw against Gabon on June 4.
Nyirenda said he was now expecting Power Dynamos striker Martin Phiri and Davy Daka of Zesco United to step into the void Mwila has left.
“But I think we have players who will take his place. I think they are also looking very good and gelling very well with the other team players,” Nyirenda said.
Meanwhile, Zambia face Ethiopia this Saturday, August 5 in a pre-CHAN qualifier friendly at Woodlands Stadium in Lusaka.
Zambia will later travel to South Africa next week to face Bafana Bafana in a 2018 CHAN final round, first leg qualifier on August 12 in East London.
The final leg will be played at Levy Mwanawasa Stadium in Ndola on August 19 that will see the winner over both legs qualifying to next January’s tournament in Kenya.