No team lineups have been published for this match yet. Team lineups are generally announced in the hour leading up to kick off. In the meantime, here's how the teams lined up in their previous fixtures:
Chelsea and Brentford last met in the FA Cup in 2012/13, with the Blues needing a fourth round replay to see off the Bees.
That tie was the last time Brentford made it beyond Round 3 of the FA Cup – they haven't made the fifth round since 2005/06.
Chelsea have been eliminated just twice in their last 20 appearances in the FA Cup fourth round (Everton in 2011 and Bradford City in 2015).
Pedro scored twice and assisted another goal in Chelsea's 4-1 win over Peterborough in the third round.
Tom Field netted twice in Brentford's third round 5-1 victory over non-league Eastleigh. All five goals were scored in the first half by the Bees.
Brentford's last win over Chelsea came in February 1939 (D1 L4 since).
Chelsea have won 13 of their last four 14 matches in all competitions, losing only to Spurs earlier this month.