Collingwood coach Mick Malthouse has called on the AFL to allow more interchange players after untimely injuries dried his side's run in their 10-point defeat to the Western Bulldogs at Telstra Dome.

The Magpies were a player down by quarter-time after Ben Reid broke his foot and then reduced to 20 fit men in the third term when fellow forward Anthony Rocca suffered what could be a serious ankle injury.

With those two gone and half-back Marty Clarke also off the ground undergoing treatment, the Bulldogs pounced by botting five goals in 13 minutes to swing the game.

Despite a gallant Magpie charge late in the game, the Bulldogs' seven-goal third term proved the difference, as Rodney Eade's side booked their place in the finals and moved to second spot by winning 15.9 (99) to 13.11 (89).

Malthouse said the injuries prevented Collingwood getting back into the match once the Doggies seized control, although Dane Swan's goal in the final term brought the Magpies within six points with about five minutes left.

"No doubt today we just didn't have the flexibility in the end to hold on and get back in the game at the right time or put more pressure on, but that's the luck of the draw under today's rules," Malthouse said.

In April Richmond coach Terry Wallace proposed that the AFL allow sides to name two reserves who could be called on during games if their teammates suffered legitimate, game-ending injuries.

Malthouse said he first called for the bench to be expanded 20 years ago, and wanted it increased to six players 10 years ago.

He said it was time the AFL moved to guarantee a level playing field, even if a league official had to rule on when reserves could be used.

"I'm of the opinion that when members pay their money, they want to see the team to be able to play - win, lose or draw - but at least play with an even playing-field if you can possibly get that," he said.

"It's very difficult to win with 20 players, it's very, very difficult because it throws your whole lot out."

Eade said he thought at half-time his side could overrun the Magpies with Reid gone, and when Rocca was injured, urged the Bulldogs to run harder.

Robert Murphy's two goals and one to Brad Johnson appeared to make the game safe, until Tarkyn Lockyer and Swan - after dispossessing Brian Lake - threatened to give the Magpies what would have been a superb victory.

The absence of Travis Cloke through suspension and Josh Fraser and Leon Davis through injury prompted Collingwood to punt on Rocca, who has been sidelined by ankle soreness.

The gamble looked a good one when Rocca snapped a goal in the third term to put the Pies clear, but he hobbled off 10 minutes later after passing to Cameron Wood.

Malthouse could not say how serious Rocca's injury was, but said both forwards would miss the game against Sydney, even though the Magpies have next weekend off.

Clarke was off for about 10 minutes after copping a heavy knock - which left only one player on the bench - but returned to play the game out.

The Bulldogs were unusually sloppy with their disposals early, but lifted through the run of Adam Cooney, Ryan Griffen and Daniel Cross, while Murphy and Mitch Hahn both finished with three goals.

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