MARK Jamar's relegation to the VFL this week has more to do with the demands of a No.1 ruckman and less about his form, says Melbourne coach Paul Roos.

Jamar is one of four omissions from the Demons' side this week, with the 31-year-old dropped along with Jack Grimes, Jordie McKenzie and Viv Michie.

Roos said Jamar had been understanding of the decision to play Jake Spencer against the Sydney Swans on Saturday night, with the big man to line up in the VFL earlier in the day against Sandringham. 

Match preview: Demons v Swans

"We spoke to Mark this morning and said, 'We're not unhappy with they way you've been playing but it's hard to do it week in, week out'," Roos said on Friday. 

"His concentration levels have got to be enormous. You've got to get to 80, 90 stoppages and then in between stoppages you've got to be active. 

"It's probably as much about the position now, it's just a really tough role. 

"We see 'Pykey' [Mike Pyke] go through it … it's almost like ruck by committee because with that sub going out, that used to be the second ruckman."

Roos added that while Spencer had earned his call up, Jamar was still part of the Demons' plans.

"The other thing is Jake has been playing really good football at the lower level and Mark was terrific in terms of accepting that," he said.

"He's still a really important part but I think it is that ruck by committee now when you look at it being such a long and tough year for those ruckmen when they're generally just one out most weeks."

After Luke Parker's public warning to Bernie Vince that he's in for a "hard day" if he lines up on Dan Hannebery, there's been plenty of interest in who the former Crow will play on.

Vince employed physical tactics that got under the skin of his former teammate Patrick Dangerfield in round three. 

Roos was bemused by the fascination about who Vince would play on and kept his cards close to his chest about who his opponent would be. 

"Bernie will play on someone. It might be Luke Parker, it might be Hannebery, it might be Josh Kennedy, it might be 'Macca' [Jarrad McVeigh], it might be Kieren [Jack]," he said.

"He might play on all of them. I think it's just a bit strange about Bernie, we've seen what he did against Adelaide and what he did against Richmond were play on opposition players and play really well. 

"The amount of hype about Bernie … we spoke about the other day that if someone from another club, maybe Sydney or Hawthorn or Freo played like Bernie no one would talk about it.

"It seems unusual that it's a Melbourne player, which is quite strange."

John Longmire and Paul Roos at the launch of the Pink Lady game at the MCG. Picture: AFL Media