I am co-commentating on this game for BBC Radio 5 Live with Ali Bruce-Ball and I cannot wait.
Macclesfield boss John Rooney did an incredible job with his side's historic win over Crystal Palace in the third round.
I watched the game back as part of my prep and, while the Silkmen had less than 29% possession, they limited Palace to very few chances and they were deserved winners.
Knocking the holders out was rightly hailed as the biggest shock in the FA Cup's illustrious history, and it would be another fantastic feat if they toppled Brentford too.
Only one non-league side has ever beaten two top-flight teams in the same FA Cup campaign - Millwall in 1913-14, when they overcame Chelsea and Bradford City.
I'd love to think Macclesfield could do it too, and if they play like they did against Palace then they have a great chance, especially on their plastic pitch.
I think Brentford will be ready for them, though, and Keith Andrews' side are having a tremendous season too.
Andrews will know he can't make too many changes here, and maybe Brentford will go on an FA Cup run themselves - they have not reached the quarter-finals since 1989, so it it is long overdue.
This is going to be a tight game but I just have a feeling the Bees will edge it.
Sutton's prediction: 1-2
Read the full predictions and have your say here