Starting on Friday, January 27th and continuing through the weekend, the FA Cup gets serious. It's the fourth round, which is when the majority of the remaining teams are those in the upper echelons of English football. That being said, there are also a number of teams from the lower leagues - including two non-league sides - holding on in the competition. Mixing the big sides with smaller ones is always a recipe for some potentially shocking results - and this weekend is no different.

Potential Shocks

Round four is full of potential shocks. It certainly features an eclectic mix of matches, ranging from all Premier League ties to non-league sides facing Championship clubs, and these are the five matches we think, offer the best chances of shocks occurring.

Derby County v Leicester City

It's easy to forget that Leicester are the current English champions - thanks largely to the fact they're enduring a torrid season this time around (Champions League campaign aside). But the fact is they are the champions and are still a Premier League side, but Steve McClaren's Derby could knock them out of the FA Cup this weekend.

The Championship team don't have many goals in their locker, but they don't concede many either - they've only let 7 in at home this season - and home advantage could be key against a Foxes side without a win on their travels in the Premier League this season.

Sutton United v Leeds United

Sutton United are the lowest ranked team left in the FA Cup.

The South Londoners are languishing in the bottom half of the National League, but have battled into the last 32 of the FA Cup, knocking out League Two Cheltenham Town and League One AFC Wimbledon in the process. It could be Championship Leeds' turn this weekend.

It's the FA Cup, anything can happen, and Sutton have a famous giant-killing pedigree in the competition - they knocked out top-flight Coventry City in round three in 1989 - and this will be the biggest game of most of their players' lives.

If they use the hostile home crowd to their advantage and play out of their skin, they could be in for a big payday and a potential round five glamour tie.

Lincoln City v Brighton & Hove Albion

The second-lowest ranked team left in the competition is Lincoln City. The Imps currently sit top of the National League and have an impressive home record this season - one they'll hope to use in their favour against Championship side Brighton.

The Seagulls are currently giving Newcastle United a run for their money at the top of England's second tier and they'll be a tough nut to crack. But, as already stated, this is the FA Cup - matches like this were made for smaller teams to shock the footballing world - and when they're having a season like the one they're having now, Lincoln have just as much chance as Brighton of getting the win here.

Millwall v Watford

League One Millwall have already dumped one Premier League side out of this season's FA Cup - they beat Bournemouth 3-0 in round three - but they face another in the form of local rivals Watford. The Hornets are similarly placed to Bournemouth in the table, but are less likely to field a weakened team at The Den and will provide a sterner test for Neil Harris' side.

That being said, Millwall are hard to beat at home and infamously have one of the most intimidating crowds in England. Combine those facts with Watford's poor form on their travels and the Lions could have another top-flight scalp to their name.

Rochdale v Huddersfield Town

Rochdale and Huddersfield have regularly found themselves in the same league over the years, but Huddersfield are currently flying high in the Championship - a tier above their League one opponents. The Terriers are in the play-off positions, but their away form isn't great - and Dale could use that to their advantage.

Rochdale's home form is great and a big reason why they're competing for promotion in League One. It's that form that makes this game the most likely to produce an upset this weekend.