Melbourne coach Paul Roos says his team simply can't afford "shocking" drop-offs in effort like the one they dished up in the third quarter of Saturday's 45-point defeat to Greater Western Sydney in Canberra.

The Demons led by 27 points at half time, only to concede 13 goals to one after the major break, including nine without reply in the third term.

Roos lamented what he believed was a dramatic decline in endeavour. "We had really good effort in the first half and then capitulated in the second, their's picked up," he said.

"That's what footy is. The most basic fundamental of footy is giving 100 per cent effort. We're not a good enough team at the moment not to. If we don't we just haven't got the talent level to go through those patches where we're not giving effort.

"They kicked nine in a quarter and six for the rest of the game. For three quarters you have effort, but if you drop off so dramatically, they've got enough talent to be able to do that."

Roos denied that fitness was an issue in the fadeout, highlighting that the Giants' collective fitness level is similar to that of his own side.

"I think everyone can run a bit harder than than they think they can run. We're no more fit or less fit than the Giants or the Suns."

Roos said that while he tried to consolidate his backline and slow the game down during the Giants' run-on, he needed to do more during the week to ensure his side is not on the receiving end of another swamping.

"Ultimately it just comes down to the message not getting through. We've just got to coach better than we are at the moment. "We just don't have a margin for error as most of the bottom teams don't have. If you play 100 per cent  you work flat out, you're still not going to beat some of the better teams but at least it gives you a chance."

Roos nominated defender Tom McDonald, midfielder Jack Viney and second-game forward Jesse Hogan as his team's three "four-quarter performers". McDonald held Giants spearhead Jeremy Cameron to a goal, while Viney held his own against  onballer Ryan Griffen. Hogan kicked  two goals and took eight marks.

Giants coach Leon Cameron said he was pleased with how his team turned the game around. "It was pleasing at half-time that no one panicked, we stuck to what we thought we were doing OK. We knew we had to tidy up on a few things, and they played some really good footy in that third quarter."