Both teams have enjoyed stellar season's in their respective leagues, with the Foxes currently being marked as title contenders in the top flight whilst Thomas Frank's side are well in the race for the automatic promotion spots in the division below.
With both sides facing tough away trips in the league just three days later, VAVEL takes a look at how both managers will look to set up for the clash at the Brentford Community Stadium.
Leicester boss Brendan Rodgers has made no secret of his desire for his side to compete for trophies since he arrived back in 2019 and with the FA Cup the missing jewel in the crown of domestic honours, it is likely that he will set up strongly.
However, form in the league has seen the East Midlanders propel themselves from targeting a top-six finish to aspirations of achieving a second Premier League title win and with a trip to Goodison Park to face Everton on Wednesday night looming, Rodgers may look to rotate to ensure his squad are as fresh as possible for the clash.
Kasper Schmeichel started in goal in the Third Round victory against Stoke City and is likely to start in-between the sticks once again. Rodgers has confirmed that Caglar Soyuncu will play in West London on Sunday which could present the chance to partner him alongside talented youngster Wesley Fofana to give Foxes fans a glimpse of what could be a colossal centre-back pairing for years to come.
James Justin has played more minutes than any other outfield player in a Leicester shirt this season and Sunday could be the perfect time to give him a well-deserved rest, especially with a more than capable back-up in Luke Thomas to call upon. On the right hand side of defence, there is every chance that Ricardo Pereira could make just his second start of the season to help him build up some much-needed match fitness.
With the Foxes expected to play their 4-2-3-1 and options in midfield lacking ever so slightly due to the injury of Dennis Praet, the first-choice midfield trio of Wilfried Ndidi, Youri Tielemans and James Maddison seems like a viable option. Nampalys Mendy is well equipped to deputise instead of Ndidi though, whilst the out of favour Hamza Choudhury could also be given a rare opportunity to start in the middle of the park.
On either flank, it would be no surprise to see the in-form Harvey Barnes in his usual left-sided position whilst on the right fans could potentially see Cengiz Under be given a rare chance to start. The Turkey international has had to make do with cameo appearances off the bench for the most part of the season, but after recovering from injury, the AS Roma loanee could be given a chance to show what he can do.
After the news broke that talisman Jamie Vardy will be ruled out for a few weeks following an operation on a minor hernia problem, Ayoze Perez and Kelechi Iheanacho know that they have a big chance to impress. Given Perez's impact in recent weeks, including a goal in the previous round, it is expected the Spaniard will get the nod but whoever Rodgers chooses will know they will have to perform to their best if they are to be considered Vardy's replacement for the next few weeks.
Starting XI: Schmeichel; Thomas, Soyuncu, Fofana, Pereira; Ndidi, Tielemans, Maddison; Barnes, Perez, Under.
Brentford will be no easy test for Leicester, with the Bees currently on a 16-game unbeaten run in the league but with a game against promotion rivals Swansea City on Wednesday, who they could move above with a win, manager Thomas Frank will no doubt have one eye on that fixture.
Two players who will certainly play no part for the West Londoners are arguably two of their key players in Josh Dasilva and top-scorer Ivan Toney with the pair both suspended after red cards against Tottenham Hotspur and Luton Town.
First-choice keeper David Raya is likely to keep his place in goal with a flat back-four in-front of him containing left-back Rico Henry as well as Charlie Goode who could replace Mads Bech Sorenson. Lining up alongside Goode in the heart of the defence is expected to be Ethan Pinnock with Henrik Dalsgaard on the right of the backline.
Moving into midfield and fresh off the back of a match-winning goal against Luton, Saman Ghoddos should retain his place in the starting 11 alongside German Vitaly Janelt as well as the ever-reliable Mathias Jensen.
With no Toney to call upon, Marcus Forss is the most likely candidate to step up in his absence with the 21-year-old coming off the bench in midweek. Alongside him on either wing is expected to be the former Charlton Athletic and Oxford United man Tariqe Fosu-Henry and Halil Dervisoglu on the other in place of first-choice options Bryan Mbuemo and Sergi Canos.
Brentford Starting XI: Raya; Henry, Goode, Pinnock, Dalsgaard; Ghoddos, Janelt, Jensen; Fosu-Henry, Forss, Dervisoglu.
If last season's Third Round encounter between the two sides is anything to go by then this game is to be a close-fought contest.
Brentford have shown in their Carabao Cup run earlier this season that they are more than capable of going head to head with top-flight opposition and will feel confident they can upset the apple cart once more this season.
The Foxes however have been in blistering form of late, especially on the road, and with the home side looking at promotion as the main goal of the season, a defeat for them wouldn't be considered too much of a disappointment.
For the East Midlanders, this will be about giving players a chance to build up fitness and stake a claim for a place for more regular opportunities, with the knockout stages of the UEFA Europa League just around the corner.
Prediction: Brentford 0-2 Leicester