More than 30 years ago the Tate was ridiculed for displaying a pile of bricks. Yesterday even its own staff were pouring scorn on its latest exhibit: a plank of wood.

Placed in the context of a gallery, the slice of oak measuring 6ft long and 6in high (1.8m x 15cm) could have its artistic roots traced back to Rodin, Simon Groom, a Tate curator, said.

The plank is by Nathan Coley, who with Mark Wallinger, Zarina Bhimji and Mike Nelson has been shortlisted for the 2007 Turner Prize, Britain’s foremost contemporary art award. The winner of the £25,000 prize will be announced on December 3.

Each artist is showing a series of works in an exhibition at Tate Liverpool, which opens to the public today.

Coley’s previous works have included cardboard models of every place of worship listed in the Edinburgh telephone directory. As part of the Tate exhibition he has installed the plank to divide his allotted space from the other shortlisted artists.

The plank, called Untitled Threshold Sculpture, explored Coley’s interest in space, the Tate said.

The problem is that visitors may not even notice it. At the press view yesterday, The Times saw two visitors trip on it. Not only had they not seen the plank, but they had to be told that it was a work of art.

Just as Tate Modern has had to employ staff to alert visitors to the “crack” installed down its Turbine Hall, Tate Liverpool will have “information assistants” warning visitors to avoid tripping on the plank. One gallery assistant was less than impressed: “I think it’s a health and safety hazard,” he said.

Dr Groom said: “The act of having to physically lift your leg to cross it announces that you are going into a different space. Entering the space may promise a revelation or enlightenment. A lot of people won’t get it. A lot of people will be curious about why it’s there.”

The bookmaker William Hill has declared Wallinger the 8-11 odds-on favourite to win.

Editor's choice

• U2 at Nou Camp Stadium, Barcelona
• The 50 Best Movie Villains
• The 15 golden rules of theatre etiquette