The holders ended a nine-year wait for a trophy by beating Hull City in last year's final and are overwhelming favourites to reach the showpiece again.
Reading are winless in five and sit 18th in the Championship and McLintock - a former Arsenal captain who made 403 appearances for the Londoners - says failing to beat Steve Clarke's men at Wembley could have long-lasting ramifications, particularly after their surprise UEFA Champions League exit at the hands of Monaco.
"I'd be absolutely astonished if they did [lose to Reading]," he told Perform. "They've already made a right mess of the European Cup against Monaco.
"If they happen to do that again it will be such a setback to them and they'd find it difficult to recover. It would cause lots of problems.
"They've got a fantastic opportunity playing Reading in the semi-finals, if they don't take full advantage of that with the players they've got and money they've spent it could be a very dangerous day for Arsenal."
McLintock believes that winning the FA Cup last season will give Arsenal plenty of confidence, but feels it would be too close a call in a potential final against Liverpool - who face Aston Villa in the other semi-final.
"It [beating Hull last season] will make them a lot more confident, obviously the more games you win the more confident you get," the Scot added. "Winning the FA Cup last year helped them this year.
"It will be touch or go to retain. It's Liverpool versus Aston Villa and I know Villa are starting to play well and get confidence but you'd fancy Liverpool against them.
"It's a strong possibility of a Liverpool versus Arsenal final and it could go either way. They're two good teams, we'll just have to wait.
"But getting to the final would be important and hopefully Arsenal will be good enough to win it."
