Several Manly rugby league players have been struck down by a stomach bug while in London preparing for their World Club Challenge (WCC) clash with Leeds.

Prop George Rose missed the NRL premiers' first UK training on Tuesday with gastric problems and a club spokesman said on Thursday a number of others, including utility Shane Rodney and back row Glenn Stewart, had fallen ill since.

"Glenn Stewart was very bad last night," the spokesman said.

Manly captain Matt Orford said those affected had been separated from their team-mates and were resting in a bid to recover for Sunday's game against London Super League club Harlequins.

"Those guys are in quarantine," Orford told AAP.

"They're probably bored staying in their rooms and away from the group, but hopefully not too many more will come down with it.

"At least four guys are sick at the moment and the doc is going to have his hands full - he gets here tomorrow."

A decision would be made on Saturday as to whether the players were well enough to face Quins in a warm-up for the WCC match at Elland Road on March 1.

Super League champions Leeds will attempt to become the first team to defend the WCC title.

Sea Eagles coach Des Hasler is expected to trial some of his younger squad members in the first half against Quins before switching to a near full-strength team for the second half.

A minute's silence will be observed before the trial game at Twickenham's Stoop Stadium and players from both teams will wear black armbands to honour victims of the Victorian bushfires.

The match kicks off just hours after Australia holds a national day of mourning for at least 208 people who died in the February 7 infernos.

"All our thoughts go out to all the victims and all the families," Orford said.

"It has been a tragedy."

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