12 Dec, 14:42
Prop Cian Healy is expected to miss the start of the 2014 RBS 6 Nations after undergoing surgery on his injured ankle on Wednesday.
Connacht Academy graduate Tiernan O'Halloran will take Matthews' place on the province's replacements bench for this evening's Magners League match at the Sportsground.
Connacht head coach Eric Elwood said: "We're all very disappointed for Keith. He's put in a tremendous amount of work and has been an integral part of our achievements this year.
"He was really looking forward to finishing the season on a high but unfortunately it looks like he'll be out for a good chunk of the year now.
"It's a good opportunity for one of our homegrown talents, Tiernan, to step up now and we'd like to wish Keith a speedy recovery."
CONNACHT (v Cardiff Blues): Gavin Duffy; Brian Tuohy, Niva Ta'auso, Troy Nathan, Fionn Carr; Ian Keatley, Frank Murphy; Ronan Loughney, Sean Cronin, Jamie Hagan, Mike McCarthy, Bernie Upton, Andrew Browne, Johnny O'Connor (capt), Ray Ofisa.
Replacements: Adrian Flavin, Brett Wilkinson, Rodney Ah You, Mike McComish, John Muldoon, Mark Dolan, Tiernan O'Halloran, Eoin Griffin.