Celtic lost goalkeeper Artur Boruc in the pre-match warm-up and then lost heavily to Aberdeen in a shock 4-2 defeat at Pittordrie on Sunday. Aberdeen's first win over the Bhoys since 2001 was a major wake-up call for manager Gordon Strachan after replacement 'keeper Mark Brown conceded four times. Strachan said, "If you don't defend well then you have to expect to lose. The way we defended in open play was more than adequate but you can't win any game if you let in four goals from free-kicks. "We will have to go and analyze our defending at free-kicks because there has got to be a common denominator if you concede four times from set-pieces. "It was a bit windy and we will have to look at whether we are doing the right thing in those types of conditions. In some conditions the way we have set up may have worked but it has not worked, that's for sure. "I know you still have to deliver the ball well and get a head on it but we are hoping that teams have to work harder to score against us. "In free play Mark Brown has not had a save to make, which is astonishing. It was a strange and exciting game and I'm sure everybody enjoyed it, apart from the Celtic supporters. "But we can console ourselves with the fact that it was one of our better performances over the last couple of weeks." Boruc injured his groin in the warm-up and faces at least a week on the sidelines. Irish defender Darren O'Dea is wanted on loan by English side Burnley, while striker Jan Vennegoor of Hesselink is looking for a contract extension at Celtic. Celtic defender Mark Wilson will be out for three weeks following an operation on his pelvis. United States international Sacha Kljestan is set to go on trial with Celtic.