ONE definitely out.

One doubtful. One set to be flown in the day before the game. That's the triple problem Neil Lennon is wrestling with ahead of Wednesday's Champions League opener against AC Milan.

As revealed in Thursday's Evening Times, Steven Mouyokolo is the man already ruled out.

And the unlucky Frenchman will miss the entire group stage campaign after undergoing surgery for a ruptured Achilles tendon, sustained in training on Monday.

James Forrest is the player who is a big doubt for Wednesday after the winger suffered a recurrence of his sciatic nerve problem while playing for Scotland against Belgium last week.

Lennon has already discounted the youngster for today's game against Hearts, but will give him every chance for the San Siro.

New signing, Nir Biton, is still trying to finalise his visa, and will fly directly to Milan on Tuesday to join up with the squad, if Celtic can collect his paperwork from the British Embassy in Turkey en route.

It's a triple headache for Lennon, but the Hoops boss is most disappointed that 26-year-old Mouyokolo - who previously suffered a cruciate ligament rupture - has again been struck my misfortune.

He said: "It was just an innocuous thing. Steven was running for the ball and we heard this pop.

"We thought he'd clipped someone's ankle. But straight away he knew there was something wrong.

"He has had a complete rupture of the Achilles tendon and has had surgery on France.

"We're just waiting to hear how well the surgery (in France) went, but we're looking at maybe six months."

Lennon continued: "It's devastating for him personally. He's worked so hard and this is a totally separate injury to the previous ones he has had.

"It can happen to anyone at any time.

"So he's just had horrendous luck, really, and we will support him all the way and, hopefully, we can get him back up and running maybe in February or March."

Mouyokolo was only signed on a one-year deal, and will have little time to convince the club he is worth another contract.

Lennon is considering looking at the free agent market to see if there is anyone suitable to bring in. But, though they could be registered for domestic games, the date for registering for the Champions League group stage has passed.

So, Lennon hopes there are no more injuries, and has his fingers crossed Forrest will get a clean bill of health to face Milan.

He said: "James's sciatic problem has flared up again.

"He played for Scotland and, looking at him in the game, I'm pretty sure he wasn't 100 per cent fit.

"We have to manage him and, at times, he has to be honest with people.

"James wants to play, but sometimes he is not doing himself any favours by doing so.

"I need a fit James Forrest because he is so important."

Biton is also very much in Lennon's plans, and the manager is desperate for the Israeli to finally start playing.

He said of the elusive paperwork: "We have a club rep going to Istanbul to pick it up.

"He will pick Nir up in Tel Aviv and he is going to join us on Tuesday.

"With him being away with his international team, we haven't been able to get a hold of his passport.

"Now we have it, we can get the visa done and get him up and running.

"He'll be available for the game in midweek."

Meanwhile, Celtic's SPFL match against St Mirren, postponed from August 10, will now be played on Wednesday, December 18.