The Parkhead side suffered further agony after their Champions League defeat at Benfica as a solitary second-half goal was enough to hand Neil Lennon’s men their third SPL defeat
McKay’s strike was the sixth the Celtic defence have conceded this season at home in the league, after having gone the whole of last season only conceding six at Parkhead.
The home side made three changes from the side that lost to Benfica in the Champions League with Kelvin Wilson, Joe Ledley and Scott Brown dropping out to be replaced by Kris Commons, Beram Kayal and Tony Watt.
Despite losing five goals at home to Motherwell on Sunday, Inverness CT boss Terry Butcher decided to make only the one change, with on-loan Arsenal midfielder Phillip Roberts replacing Graeme Morrison in the starting line-up.
Neil Lennon’s side started the brighter of the two, with both Commons and Victor Wanyama having efforts at goal, but neither doing enough to trouble Antonio Reguero in the Inverness goal.
Inverness’ best chance of the half came when Owain Tudur-Jones played in Andrew Shinnie, but unfortunately for the Scotland international his shot went well wide of Fraser Forster’s goal.
As the half came to a close, Celtic had two superb chances in order to take the lead going into the break as Hooper played in Commons on the right hand side of the penalty area, but the 29-year-old’s effort was wasteful and ended up going out for a goal kick.
The home support were left frustrated again by their side as a superb through ball from Kayal found Mikael Lustig racing into the box, but the Swede could only direct his strike into the side-netting of Reguero’s goal.
Celtic continued on the front foot at the start of the second half, but they could not find a way past the Inverness defence, as Commons was forced to try his luck from long range but could not find the target.
Inverness took a shock lead after some superb play by Roberts on the right hand side of the box saw the midfielder beat two Celtic defenders before playing the ball across to McKay, who had the simple task of knocking the ball into the net.
The lead could have been extended as Andrew Shinnie played the ball from the right wing towards goal and Tudur-Jones managed to get a touch onto the ball to direct it towards goal, but Forster saved easily.
Celtic started to pile on the pressure again, with Georgios Samaras having a header saved by Reguero, before the Spanish keeper then had to save from Gary Warren in order to prevent an own goal.
Inverness should have wrapped up the three points as they once again broke on the counterattack, with McKay hitting the bar, before the rebound dropped to Aaron Doran and he somehow managed to hit Efe Ambrose on the line.
The visitors continued to defend for their lives during the closing stages of the game and they managed to survive and leave Glasgow with all three points.