The Wests Tigers are desperately hoping superstar Benji Marshall pulls up pain-free after the injured playmaker completed a final training session for Friday night's NRL's do-or-die semi-final against Canberra.

Television footage showed Marshall running freely at a closed session, but it is how his injured knee responds on Friday morning that will determine whether he takes his place against the Raiders.

Coach Tim Sheens said he will give his key man until the last minute to prove he is fit but added, if Marshall pulled up stiff, it would be hard to pick him.

"We'll see how he goes after training," Sheens said on Thursday.

"I'm keeping an open mind at the moment.

"Every senior coach gives every player, let alone a key player, as much time as possible.

"We've got about six (players) that we're carrying at the moment but we've got contingencies."

Those six include forwards Gareth Ellis (back) and Bryce Gibbs (knee) and centre pairing Chris Lawrence (jaw) and Blake Ayshford (virus).

Sheens described Lawrence and Ayshford as "very doubtful", the latter finally joining the squad after being cleared of glandular fever.

Tigers chief executive Stephen Humphreys also appeared more hopeful than confident of Ayshford playing at an announcement about an upgrade for Leichhardt Oval.

"He's certainly getting better, he's feeling better, but he's got a bit of a way to go," Humphreys said.

"Obviously suffering that kind of illness, it's drained his energy levels and so that's as much of a concern as anything else."

Raiders co-captain Terry Campese said the home side, who closed their training session for the first time this year, were preparing for Marshall to play.

"(Marshall) has got the wood on me twice this year so I've got one game to get it back and this is the game that counts," the five-eighth said.

"They're probably the best attacking side in the comp so if we are down on attitude or we don't bring our best game they'll just score five tries in a matter of 10 minutes.

"We've got to turn up with our heads on and make sure we are at our best defensively."

Canberra have no major injury concerns, with co-captain Alan Tongue returning from a calf injury.

His defence will help lift a side also set to be buoyed by a crowd of 27,500 Green Machine fanatics.

The sell-out crowd has forced the one-town club to send a message to fans: "Get there early".

Meanwhile, injured Tigers utility Tim Moltzen has categorically ruled himself out of any involvement in the finals, regardless of whether his side makes it to the October 3 decider.

Moltzen is on a six-month recovery from a ruptured anterior cruciate ligament.

"Everything's looking positive, for next year that is," he said.

"When we decided to take the longer approach to the operation for the knee, it was always known it was going to be a six-month injury and I haven't thought otherwise.

"It's only been five months at the moment so we're a month away."

Moltzen is confident the Tigers can get the job done at Canberra Stadium.

"We've travelled down there a couple of times over the last two years and come away with wins so it's definitely a trip we're used to," he said.

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