Kasper Schmeichel was missing from Celtic’s squad for Sunday’s Old Firm at Ibrox.The 39-year-old has come under fire from fans in recent weeks amid a string of errors.Viljami Sinisalo was named as the starting goalkeeper for CelticGettyFinland international Viljami Sinisalo was named in goal for the clash against Rangers.The 24-year-old had replaced Schmeichel in the starting XI for Thursday’s Europa League clash against Stuttgart.He was widely expected to keep his place following a strong performance.However, what was not expected was to see Schmeichel absent from the entire squad for Sunday’s Old Firm.Third choice goalkeeper Ross Doohan was named on the bench as the team news was announced before kick-off.Celtic boss Martin O’Neill later confirmed that Schmeichel is missing from the squad due to illness.O’Neill said: “He was poorly this morning and we decided this was it.“I thought Sinisalo did well on Thursday evening, so I just thought I’d leave it as that.“That [Sinisalo’s good performance] does [make it easier], but let me put it this way, Kasper has been fantastic in the two spells I’ve been here.“I’m pretty pleased to have both of them.”Schmeichel has been booed by Celtic fans in recent gamesGettySchmeichel boosThe Premier League winner was booed by Celtic fans following errors in their 4-1 defeat to Stuttgart in the Europa League.He was jeered every time he touched the ball following that disastrous first leg defeat at Celtic Park.Former Aberdeen and Denmark goalkeeper Peter Kjaer believes that he will have been affected by the boos.He said: “I was really surprised when I head the catcalls from Celtic fans towards Kasper Schemichel. When your own fans are on your back, it is very unusual.“It doesn’t strike me as typically British. In Scotland I never experienced it, not just towards me, but in general I didn’t experience it. You rarely experience it.“I have no doubt that Kasper is mentally strong.“But no matter how we twist it, it’s something that affects a person. That’s how I would have felt.“However, I don’t think it’s the right time to look for a new keeper for Denmark though.“For me, it would be deeply strange if you change ahead of the first play-off game. I’m not the Denmark manager, but for me it would be crazy to change keeper, especially when we have so many injuries and suspensions in defence.“I don’t doubt for a second the qualities of back-up goalkeepers Filip Jorgensen or Mads Hermansen. But we haven’t seen them play for the national team.“Kasper has made mistakes and will make some again, but you know what you are getting with him – someone who has won many caps and knows what he’s going to face.“I see it a bit like a boxing match, where the first choice is the world champion. He has to be knocked out before you can win the belt. It’s not enough to run out of time, you have to knock him out.“So be careful about throwing Kasper out of our plans and saying he is finished.”Confirmed Old Firm teamsRangers: Butland, Sterling, Souttar, Fernandez, Rommens, Chukwuani, Raskin, Skov Olsen, Moore, Naderi, Chermiti.Subs: Kelly, Meghoma, Djiga, Tavernier, Aasgaard, Bajrami, Gassama, Diomande, Miovski.Celtic: Sinisalo, Araujo, Murray, Scales, Tierney, McGregor, Oxlade-Chamberlain, Yang, Nygren, Maeda, Adamu.Subs: Doohan, Cvancara, McCowan, Saracchi, Tounekti, Arthur, Hatate, Forrest, Donovan.