Liam Brady has warned his Arsenal to expect the unexpected in their Champions League playoff against Celtic.

Brady, the former Celtic manager who is Arsenal's head of youth development, told the Guardian: "Our players have been all over the continent but they will never have experienced anything like it. The atmosphere at Celtic Park is unique. Arsenal have to go and cope with the environment and the pace Celtic will play at and the tremendous following they have. It is different to what you get in mainland Europe. Our players will have to be prepared for that.

"The Celtic Park leg is the unknown aspect of this tie. For intensity, it will be a bit like the Liverpool-Arsenal quarter-final from a couple of years ago."

Celtic's dramatic away win at Dynamo Moscow, to set up this tie , suggests they are very much in the mood to upset the odds in this European campaign. Brady is conscious of how keenly Celtic respond to adversity.

"If you match the two teams up player for player, there is no argument about who is the strongest. You have to fancy Arsenal big-time, but Celtic have proved they can raise their game when they are underdogs," he said.

"They have started the season well under Tony Mowbray. He gets his teams to play football ... But I think there will be plenty of aggression, too. You need to be on the inside to realise how big the expectation is ... which I discovered during my two and a bit years there. It is like leading a community rather than just being a football manager."

The high stakes will only add to the tension.

Brady said: "Both teams are desperate to get into the group stages, and possibly beyond, for the financial rewards as well as sporting reasons. Arsenal are under pressure to get to where the team has been for several years. Celtic badly need it because they get very little domestic revenue in Scottish football."