Gold Coast coach Guy McKenna blames the AFL's controversial new substitute rule for defender Michael Coad straining a hamstring against Melbourne at the Gabba on Sunday.

McKenna said Coad had been suffering cramps and they had endeavoured to rest him.

Under an ideal scenario, McKenna said he would not have forced his defender to keep playing.

However as the Suns had already activated their substitute, the coach said he had little choice but to keep Coad in the field.

"(We were) trying to get him off with cramp, which we did a few times, but he went back out, due to rules and regulations, he's now done a hamstring," McKenna said.

"Some people look at the game and think it's great, the sub rule, well little things like that has cost Coady a two- or three-week hamstring.

"Dan Gorringe was subbed off so we had to send him (Coad) out there."

Senior coaches have come out in force to criticise the AFL for this year reducing the interchange from four players to three and a substitute.

A player who is subbed out of a game is unable to return.

The Suns may have lost Coad for a couple of matches at least, but McKenna said champion midfielder Gary Ablett would be available for next Saturday's clash with Port Adelaide at AAMI Stadium.

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