Ollie Magern has been pulled out of the Grand National by his trainer Nigel Twiston-Davies after reporting lame.

Twiston-Davies discovered the problem on Wednesday and Ollie Magern is unlikely to run again this season.

"He has had those problems in the past and now it's happened just a few days before the National," said the Gloucestershire trainer Twiston-Davies.

Ollie Magern's place goes to Philson Run, who came fourth in the 2007 National.

Philson Run, the Nick Williams-trained 12-year-old, had been 41st on the weights, needing one of the top 40 to pull out in order to get a run.

Tom Mullins believes his Grand National hope Chelsea Harbour ticks all the right boxes for Saturday's big race.

The eight-year-old was a smart novice last term and won a Grand National trial at Punchestown in February.

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He will also have the assistance of Davy Russell, currently involved in a titanic struggle with Ruby Walsh for the jockeys' championship in Ireland.

Mullins said: "I suppose his best wins have come on terrible ground but he's won on all types of ground."

"He won over hurdles on good ground though and some people think he might jump better on better ground and I wouldn't disagree with them either.

"We've ticked all the boxes up to now and hopefully nothing happens between here and Saturday."

Willie Mullins is delighted Paul Nicholls failed in his attempt to lure Walsh away from National specialist Hedgehunter.

Walsh's loyalty means Nicholls's best hope, Turko, will instead be ridden by Richard Johnson.

Hedgehunter, the 2005 winner, was second a year later and ninth 12 months ago. He ran a pleasing race behind Afistfullofdollars last time, finishing in front of stablemate Snowy Morning.

"I thought he (Walsh) might ride the other horse (Snowy Morning) but he's elected to ride Hedgehunter," said Mullins.

"I'm happy as Ruby knows him very well and hopefully it will be a good result.

"I think he is coming back to himself and he appears in good form, he worked this morning and Ruby came to ride him.

"He loves the track and if it keeps drying that will be in his favour. If it rains that will probably favour horses with lighter weights."

The slight confusion over Timmy Murphy's intended mount has been cleared up with David Johnson's retained rider plumping for second-favourite Comply Or Die.

The nine-year-old will be one of five runners for David Pipe, whose father was successful with Miinnehoma in 1994.