The Glebe Park men have put together a seven-game unbeaten run, winning five and drawing two in the Irn-Bru Second Division since former Dundee United star Ray McKinnon took over in October.
With Saints already having made the last four of the Scottish Communities League Cup, McLean believes the experience garnered on that run to Hampden will stand his side in good stead.
The Buddies midfield ace said: "There is no way we'll underestimate Brechin. You only have to look at their record under Ray to see they are a very well organised side who are playing with a lot of confidence.
"The other thing is that if a side is going well it doesn't matter what league they are doing it in.
"The bottom line is Brechin will be playing with a lot of self-belief and they will come to St Mirren Park knowing they are the underdogs and that there is no pressure on them.
"When teams come with that type of attitude they are dangerous.
"And we won't know what way they will set up until the first whistle. When you are up against a team you have not played before there's an element of the unknown to it.
"But that is what makes cup football so entertaining for the fans and enjoyable to play in. We just have to make sure we get the right result."
With Saints having taken five goals off Second Division Ayr and claimed a one-goal win over Hamilton en route to the last four of the League Cup, McLean has no doubt his side have the nous to take care of the Glebe Parks side's challenge.
He said: "Last season we lost in the quarter-finals of the League Cup at home to Ayr and we just found it very hard to break them down.
"Fair play, they came with a plan and they made it work. But we showed when we faced Ayr this season in the same tournament and even more so against Hamilton, that if teams come to sit in we have the ability to break them down that bit better now.
"Brechin carry a goal threat as they have demonstrated in recent weeks, so they may come to St Mirren Park and have a go and that would suit us.
"But if you get a team from a lower league at home, you must take care of business."
Meanwhile, midfielder John McGinn has agreed a three-year contract extension. The 18-year-old made his first-team debut as a substitute last month and has started the last two matches.