Sharks coach, Rob Du Preez says he has been impressed with the way the Durban born 24-year-old has stepped up every time The Beast has been absent this season.
Du Preez says the unavailability of Mtawarira who is struggling with a knee injury is a massive blow to his side.
It has been a challenging week for the Springbok veteran who has been criticised for his comments made in his upcoming biography about former national coach, Peter de Villiers.
Du Preez says they are not sure when he will be available to play again.
The Brumbies are the form team in the competition with six wins in a row under their belt.
Du Preez singled out their approach at set-piece time and admits that is an area his side has worked on specifically ahead of the clash in Canberra. – Report by Thahir Asmal