Blue Toon's back line must stand up to Queen's Holmes
Cooper said: "Big Rory was a handful last week. I know Derek Holmes from our days at Ross County and he is capable of doing similar damage so our defenders need to be up for the challenge. This is great opportunity for us to get to a national final for the first time and we are determined to do well."
Defender Bobby Mann is still missing and fellow ankle injury victim, midfielder Nicky Clark, is also out. Striker Connor Gethins has lost his battle against a thigh injury.
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Hide AdQueen of the South boss Kenny Brannigan is wary of facing the Second Division side. He said: "This is going to be a really hard game, especially with the supposed underdogs being at home."
The midfield duo of Rocco Quinn and Allan Johnston have been passed fit but striker Sean O'Connor is out injured. Midfielder Steven McKenna is banned.
After last season's Scottish Cup final run, Ross County manager Derek Adams is looking to see off Partick Thistle in tomorrow's live BBC ALBA TV game. Adams said: "To reach the Scottish Cup final and then follow that up with a Challenge Cup final would be fantastic."
Striker Steven Craig may return from a hamstring injury but Andrew Barrowman is still out with a broken foot.
Thistle won 2-0 in Dingwall last Saturday and assistant manager Ian Maxwell said: "Winning last weekend has made training a lot more upbeat but it will be difficult to beat Ross County twice on their patch in successive weeks."
Ryan MacBeth is fit again but midfielder David Rowson is doubtful and Simon Donnelly is likely to miss out due to a back injury.