Groundsmen are working around the clock to improve the playing surface, which was slammed by former Liverpool midfielder Steve McMahon.

The pitch has several bare patches and is very bumpy. Blocks of frozen grass shipped in from Slovakia have not bedded down as hoped and the state of the surface is giving real cause for concern.

Wednesday's match between Manchester United and Chelsea is at the same stadium where England played their Euro 2008 qualifier against Russia on an artificial pitch last year.

English head groundsman Matthew Frost said: "It is not like one of the better Premier League pitches, far from it.

"Unfortunately, things didn't work out. The ball may not travel perfectly like it would on a pitch that has been in situ for some time. There might be a bit of a bobble."

But McMahon was more scathing in his assessment of the pitch, claiming it would be "dangerous" for the players.

"It is awful and embarrassing," he said. "There are undulations and, to be frank, it is very dangerous for the players if it stays the way it is. The players won't be happy."

Meanwhile, the referee for Wednesday game is the man who awarded a controversial and decisive goal against Chelsea in their 2005 Champions League semi-final second leg at Liverpool.

Slovakian Lubos Michel was criticised by former Blues boss Jose Mourinho after he ruled that Luis Garcia's shot had crossed the line in front of the Kop at Anfield.

The linesman who signalled to Michel that it was goal, fellow countryman Roman Slysko, is again one of his assistants, along with Martin Balko.

Mourinho called Garcia's strike "a goal from the moon" and insisted it never crossed the line, an opinion supported by television replays.

Michel, 40, has been in charge of one Chelsea Champions League match since that controversial moment, when he officiated their 1-0 group phase defeat to Werder Bremen.