The ACT Brumbies' hopes of reigniting their season have been dealt a massive blow after Wallabies back Matt Toomua was ruled out of the club's match against the Pretoria Bulls.

Toomua suffered a knee injury last weekend and is set to miss what looms as a make-or-break match on Friday night for the Brumbies finals hopes.

Versatile back Robbie Coleman will shift to inside centre and James Dargaville will be called up for his first start of the season on the wing.