Manager Neil Lennon revealed that Mouyokolo won't play again until the New Year after suffering a "devastating" rupture of his Achilles tendon in training earlier this week. The French centre-half had been providing cover for Virgil van Dijk, Efe Ambrose and Charlie Mulgrew in central defence and had played against Aberdeen last month.
Lennon admitted the 26-year-old's injury left his defensive options short. "We may look for someone else. We are alright at the moment, but it may be important to bring someone in until January.
"It is a devastating blow for Steven. This injury is totally separate to his previous injuries. It could happen at any time but it was just so innocuous - he was just running for the ball and his heel popped. He has completely ruptured the Achilles. It can be a worrying injury. At least it is a clean rupture, which is good. So he is going to be in a pot [plaster cast] for about a month or two but the physios are pretty confident he will be back in the New Year at some stage."
James Forrest has a sciatic nerve problem which has ruled him out of today's SPFL Premiership game at Hearts and will need to be continually monitored for the foreseeable future. Lennon hinted that the winger had sometimes done himself a disservice by playing when instead he should have admitted he was not ready. "He played for Scotland against Belgium and, looking at him in the game, I'm pretty sure he wasn't 100% 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. We are going to manage him over the next few weeks as this is an important few weeks for the club. I need a fit James Forrest because he is so important.
"Basically, it's an inflamed nerve which runs from the back down through the legs. It's hampered him for a while. We got him up to full speed and you could actually see him getting stronger as the game went on against Shakhter Karagandy, so that's the James we want to see."
Teemu Pukki trained with Celtic for the first time yesterday and the Finnish international striker could make his debut at some stage of the game at Tynecastle. Lennon praised Hearts manager Gary Locke for already taking the club to minus-eight points in the table after starting the season with a 15-point deduction for being in administration. "Clubs just ahead of Hearts will be looking over their shoulders," he said.
Lennon, assistant Johan Mjallby and first team coach Garry Parker will fly from Edinburgh by private jet after the match in order to watch next Wednesday's Champions League opponents, AC Milan, play at Torino in Serie A. Celtic's match kicks-off at 12.30pm and the game in Italy starts seven hours and 15 minutes later.
Celtic have won three of their four league games so far and dropped two points at home to Inverness Caledonian Thistle. "Last season I got the feeling that maybe some of the players were saving themselves for the Champions League games," said Lennon. "I've made it pretty clear if I detect that this year, then there is a distinct possibility they won't play in the Champions League.
"I'm not giving ultimatums out. I just think it's important they play at full steam in the league games. They have got plenty of time to recover - Sunday, Monday and Tuesday. We won't do a lot of training in between."
New Israeli signing Nir Biton will be unavailable today but could feature against Milan after the club make a complicated completion of his work permit application. Someone from the club will collect Biton in Tel Aviv and then take him to Istanbul where the paperwork will be completed and the work permit granted. Celtic have needed his passport but have been unable to take it while he was on international duty.
Since Lennon was last in a dug-out, a fortnight ago, he has rubbed shoulders with some of football's coaching aristocracy. One of the belated perks of reaching the last 16 of the Champions League last season was being invited to a get-together of managers and head coaches whose clubs reached the later rounds of last season's Champions and Europa Leagues. "It was excellent. There was talk about the Champions League, its format, financial fair play and refereeing: which I was very interested in! It was a fantastic experience for me. There was a live link to Sir Alex Ferguson as well from Old Trafford. He still has a huge influence on things.
"It's like the United Nations. You sit around in a big room around a big desk with your headphones on and interpreters all sitting through the back. There's a big screen and topics coming up and then it's thrown to the floor. It was interesting seeing everyone's perspective on things.
"I think Michel Platini has introduced this as he's a football man and wants to help managers along the way. If there's anything the managers feel needs changing he will try and push that through. You turn up and are sitting at dinner with Rafa Benitez, Antonio Conte and Andre Villas-Boas. It was very, very cordial and just a great experience. I found Benitez to be a very affable guy which is probably different from his public persona. He was very, very good with me.
"It meant so much to go there knowing we are in the Champions League. I'd have been going with a red face had we gone out to perceived lesser opposition in the Kazakhstan champions."