GARY THORNTON says his Doncaster side have two big reasons to go all guns blazing at Bootham Crescent tomorrow night - to build much-needed momentum for the play-offs, and avenge their March mauling by his old club.

The Dons still need a point from their last two games to be mathematically certain of a top-five finish but they are virtually there given their point-difference is far superior to Hunslet's - meaning it would take two big defeats to York and London Skolars and a big Hunslet win at Rochdale for the Hawks to usurp them.

Thornton nevertheless admitted sealing their semi-final berth with victory at his former club York City Knights would make it all the sweeter.

"From my point of view, I was very disappointed that day," he said of their 46-16 reverse to the Knights earlier in the year, in which no fewer than four ex-Dons also scored tries.

"We were understrength and well under par, while York were very good - one of the best performances from any team in League One this season. They put us to the sword.

"I'm still smarting from that. It was my first game against York since leaving York and we let ourselves down.

"I want to show York and James Ford (who replaced him as Knights boss) what we're really about as we didn't do that on that day.

"The players feel the same."

He added: "It's not yet definite we're in the play-offs either so we need something, and we also want to build momentum for them.

"We beat Keighley but then lost to Rochdale. We want to go in to the semi-finals in form.

"We can also still finish above York if we win both our games so there's still a lot to play for, while damage limitation is another factor."

That last comment refers to the fact Doncaster are down to their last 19 players tomorrow, which includes Iafeta Paleaaesina should he be freed up on dual-reg by Hull - which seems likely after the big Kiwi prop was left out of the Challenge Cup winners' squad that takes on Wigan on Friday.

The Dons' injury list is now up to ten, after former Knights enforcer Joe Pickets (knee) and Mason Tonks (ankle) got crocked in Sunday's defeat at Rochdale.

Said Thornton: "We're down to the bare bones so we don't need any more injuries. But first and foremost, we have to make sure we qualify."

As things stand, York and Donny - barring a major slip-up - will finish fourth and fifth, in either order.

In the play-off semi-finals, whoever comes fourth will go to the team in third.

Whoever finishes fifth will visit the team that loses the promotion final between the top two.

Toulouse have won the league and will host that final, against Barrow or Rochdale, who are level on points in second and third.

Barrow must also go to Toulouse this Sunday for their last Super 8s fixture while Rochdale host Hunslet - meaning the Hornets are favourites to finish second.

That means finishing fifth rather than fourth might be preferable, to avoid form team Barrow in the semi-finals - on the assumption runaway leaders Toulouse don't slip up.

But Thornton said: "There are many permutations so you can't plan for anything like that.

"To win the grand final you have to go away and beat these teams at some point.

"What will be will be, whether we get Barrow or Rochdale, or even Toulouse.

"We just want to win every game and get some momentum for the semi-finals.

"We're looking no further than York. Then we'll look at London Skolars, then review the situation after that."