Charlie Nicholas insists as many as SIX Celtic first-team stars are letting Neil Lennon down.

The former Parkhead star fears the Hoops have become their own biggest threat to a historic Ten In A Row triumph.

Lennon's side trail rivals Rangers by six points at the Premiership summit, although they do have a game in hand.

But Nicholas reckons that could count for little if Celtic don't get their act together fast.

He told The Express: "The biggest threat to Celtic's charge for Ten In A Row is themselves.

"They are on the edge. It is not so much a case of worrying about the challenge of Rangers, but more about their own form.

"They need to sort themselves out before they even consider what is happening across the other side of the city.

"Celtic are in a hugely dangerous position.

"Celtic are in the midst of a run of games in which they are vulnerable and look stretched to the limit.They are on shaky ground.

"Lennon was brought back to the helm because the club knew their squad was the strongest in the country and he would guide them to success.

"The manager insists there is no panic but if they lose to Lille in the Europa League on Thursday and get knocked out of the

"Scottish Cup - killing their hopes of a fourth successive treble in the process - then it would transform the whole outlook of the season.

"That would put things under serious review, and I'm not referring to Lennon's job.

"I mean, who is the manager going to trust in terms of his players and the formation he deploys?

"There is a long way to go in the title race.

"This is not the time to hit the panic button, but Lennon has a lot of pressure on him because there are five or six players in his starting line-up who aren't doing the business."

Nicholas also remains baffled by the club's summer signing business, insisting Shane Duffy does not fit the 3-5-2 shape Lennon has deployed for much of the season.

He added: "The onus was on Celtic to make themselves stronger over the summer and to be able to adapt to a 3-5-2 or 4-4-2, or any other formation.

"Lennon seems to prefer a back three but he has brought in players who don't necessarily perform best in that formation.

"Shane Duffy is one of them. He looks lost in a back three.

"This was a guy who was signed as a big, physical presence who would bully strikers. However, Celtic don't need a bullying centre-half - they need a ballplaying one."