Both sides have had a mixed bag of results so far this season in their league campaigns and whilst the Championship remains their priority, both teams would love a cup run.
• Team news
The only absentee for Millwall is midfielder, Billy Mitchell, who remains sidelined as he recovers from an injury.
Irishman, Troy Parrott, could be given a chance to impress after he was an unused substitute in the Lions midweek win over Huddersfield Town.
Ryan Woods, Scott Malone and Jed Wallace should all start in midfield with defender Alex Pearce likely to be given a run-out in Millwall's back three.
The Robins have been cursed with injuries this season with Andreas Wiemann, Callum O'Dowda, Jamie Paterson, Jay Dasilva, and Steven Sessegnon all unavailable.
Liam Walsh, Nathan Baker and Joe Williams are all doubts despite returning to training.
Antoine Semenyo could be gifted a start for the Robins after coming off the bench against Norwich City in the week. Adrian Mariappa also looks likely to start after playing a full 90 in their last FA Cup tie.
• Predicted lineups
Bialkowski, Wallace, Hutchinson, Pearce, Malone, Williams, Leonard, Woods, Wallace, Smith, Parrott.
Bentley, Mariappa, Kalas, Mawson, Rowe, Semenyo, Nagy, Bakinson, Adelakun, Martin, Diedhiou.
• Ones to watch
Millwall - Jed Wallace:
Lions wide man, Wallace, has been one of Millwall's best assets for a number of seasons. His quality in front of goal could be key for Rowett's side and his ability from dead-ball situations should be monitored by the Robins.
Wallace has six goals and two assists to his name this season which makes his return the best in the Millwall squad this campaign.
The 27-year-old likes to run with the ball and will feed consistent service into the strikers and will certainly be a handful if he is on his game.
Bristol City - Famara Diedhiou:
Senegalese international, Famara Diedhiou, boasts a big presence up top for the Robins. His height and power combined with his excellent ability to hold the ball up and bring others into play can terrorize opposition defenses.
The 28-year-old has four goals this season but he brings to more than goals Bristol City's attacking play.
When they are defending, Diedhiou is their out ball and if he performs how he can, he will be a thorn in Millwall's defense on Saturday.
His determination to make the box also makes him a great threat and with his finishing ability, he could be the difference on the weekend.
• Previous meetings
These two sides most recently met in December. Millwall won 2-0 with goals from Tom Bradshaw and Mason Bennett sealing a comfortable away win for the Lions.
Bristol City have won just once in the last nine meetings between these two. That win came back in December 2019 when two late goals from Paterson and Diedhiou meant the Robins came from behind to win 2-1.
Last time out:
• Where to watch
This game will kick-off at 3pm on Saturday 23 January 2021. The game can be watched on the BT Sport Extra 6 channel and it will not be broadcasted on either team's respected streaming programs.