Fremantle coach Mark Harvey has renewed his call for an expanded interchange bench in AFL games by claiming it will only add to the spectacle for supporters.

The Dockers were a player short for the entire second half after Garrick Ibbotson went off the ground with a dislocated right shoulder in the second quarter, and also had defender Chris Tarrant roll an ankle in the dying seconds.

The injuries had no bearing on the game, as Fremantle won 17.11 (113) to 9.15 (69), but Harvey said it was time the AFL expanded the bench to cope with the impact the speed of the game has on sides.

Harvey called for the introduction of a substitute player as an addition to the four-man interchange bench who could come into the game if a teammate suffered a game-ending injury.

Substitutes were successfully trialled during the pre-season competition.

"These games are played at frenetic speed and you only have to look at the amount of players who are cramping ... we might have to look at extending the bench. That's my view," Harvey said.

"Have a look at five. We lost Ibbotson early today which then puts pressure on the other guys to be able to play out there for longer periods, so why not?

"I think it's a great spectacle, the game, so why not add to what we're doing? It won't detract from the game, it will only add."

Tarrant and Ibbotson will be assessed this week to see the extent of their injuries before the Dockers play Geelong next Sunday.

Collingwood are hopeful a knee injury to defender Ben Johnson is not as bad as first feared.

Johnson, who missed a large chunk of the 2009 season with a broken leg, had to be carried from the ground in the second quarter of Saturday's win over Melbourne at the MCG.

There were initial fears of an anterior cruciate ligament rupture to the 28-year-old's right knee.

But the Magpies said on Sunday that club medical staff were hopeful there was no structural damage, although more would be known after he had scans on Monday.

Coach Mick Malthouse said after the game on Saturday that Johnson, who turns 29 on Monday, was in pain from a "massive abrasion" on the side of his knee.

Meanwhile, West Coast utility Mark Nicoski looks set for a significant stint on the sidelines after injuring his troublesome right shoulder against Port Adelaide at Subiaco on Saturday night.

The 26-year-old was forced out of the match late in the opening term.

He has already battled two previous serious shoulder injuries in the past three years.

And Brisbane's Jed Adcock will undergo scans after injuring his quad in the second quarter of Thursday night's win over Carlton, putting him in doubt for Saturday's clash with Port Adelaide at AAMI Stadium.

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