Tony Pulis's side have defeated Bristol City and Peterborough to reach the last 16 of the competition, where they will play Reading at the Madejski Stadium on Saturday afternoon.
However, if West Brom were to reach the final at Wembley at the end of the season, McClean would be forced to rearrange his wedding - which is scheduled to take place 24 hours before the date of the showpiece in North London.
The Republic of Ireland international has admitted that his partner wasn't filled with joy when the conflicting dates came to light, but hopes that he can enjoy a memorable month both on and off the pitch.
The 26-year-old said: "We booked the wedding last year when I was at Wigan for May 20 and the FA Cup Final falls on May 21, so she’s hoping we get beat every time we play a cup game.
"She’s the only person who doesn’t want to see us reach the final. We might have to get married at half-time or after the game, maybe, should we get there. You can imagine when I told her the final was the day after our wedding date - she wasn’t exactly jumping for joy, put it that way. But she understands.
“I’ve a lot to look forward to this summer so, hopefully, it’s a time I can look back on with a lot of happy memories in the future."
Since leaving Wigan Athletic after their relegation to League One last summer, McClean has become a first-team regular since moving to The Hawthorns.
The midfielder has featured in all but three of West Brom's games in the Premier League, scoring two goals.