The champions are on course to retain their title after opening up a five-point gap at the summit, while Leganes are focused on moving further clear of the dropzone.
Barcelona booked their place in the quarter-finals of the Copa del Rey with victory over Levante on Thursday evening, but their progression did not come without some controversy.
A second-half strike from Lionel Messi added to his two assists for Ousmane Dembele in the first half, giving Barca a 3-0 win on the night and a 4-2 victory on aggregate, having lost the first leg 2-1 last week.
Prior to the match it emerged that Levante are to lodge an official complaint to the Spanish Football Federation over irregularities in Barcelona's starting lineup last week, as youngster Chumi played nearly an hour, despite being suspended after picking up a fifth booking in the Segunda Division B.
For now, though, Ernesto Valverde's side are in the hat for the last eight and remain on course for a treble, having opened up a fairly comfortable lead at the La Liga summit and made it through to the knockout rounds of the Champions League, where Lyon await over two legs.
Barca can focus on the league for the time being, with games against Leganes, Girona, Valencia, Athletic Bilbao and Real Valladolid over the next month presenting Valverde's men with a good chance to put further distance between themselves and the chasing pack.
After losing at home to Real Betis and drawing at Atletico Madrid in successive matches in November, Barca have since taken 18 points from 18, scoring 18 goals and conceding just one - that coming in a 2-1 win at Getafe two weeks ago.
No side in European football's top five leagues can boast a better run of form than the Spanish champions, who have won the league title in 12 of the last 14 seasons in which they have finished as winter champion, as is the case in 2018-19.
Finding a way to stop Barcelona is proving incredibly difficult for opposition sides right now, with the Catalan giants' tally of 53 goals for the season only bettered by Manchester City in the elite divisions, so Leganes must be at their absolute best when they arrive at Camp Nou.
Recent form in La Liga: WWWWWW
Recent form (all competitions): WWWLWW
Leganes should not be completely written off ahead of Sunday's match, though, having pulled off a shock victory against Barca when the sides last faced off in the league four months ago.
That was Barca's first defeat of the season and just their second ever under Valverde in the league, while at the same time giving bottom-side Leganes a major lift in their mission to dodge the drop.
Los Pepineros are in a far healthier position now, with four wins and six draws in 13 matches since that memorable triumph taking them up to 13th, three points and five places above the dotted line.
Mauricio Pellegrino's side are just as close to Real Sociedad in eighth as they are to Rayo Vallecano in 18th, in fact, and they face to two teams in relegation danger in their next three matches after this daunting trip to Catalonia.
Leganes's away form has been a huge positive in recent weeks, avoiding defeat in four of their last six away games - as many unbeaten games as they had in their previous 20 matches away from home in the top flight.
Breaking down the visitors will be no easy task for Barcelona, either, as they have the seventh-best defensive record in the division, conceding just one goal more than the league leaders across their first 19 matches
Only Atletico (58) have faced fewer shots on target than Leganes (66) in La Liga this season, but their tally of 17 goals scored is the joint-worst in the division. Holding out for a goalless draw may therefore be Los Pepineros' best bet of keeping their momentum going.
Recent form in La Liga: WDDDLW
Recent form (all competitions): DDLLWW
Valverde was forced to start Messi for the second leg of his side's Copa del Rey tie with Levante following defeat in the first leg, but Luis Suarez spent most of the night on the bench and the likes of Gerard Pique and Sergio Busquets were fully rested.
All three of those players are expected to slot back into the starting lineup on Sunday, but Valverde has a big decision to make with regards to who drops out to make way for Suarez.
Dembele netted twice against Levante, albeit with two fortunate finishes, and will surely retain his place, meaning that Coutinho could again drop down to the bench.
In terms of the visitors, Pellegrino has a number of injury problems and suspensions to contend with, including the absence of Guido Carrillo for the rest of the month because of an ankle complaint.
Barcelona possible starting lineup:
Ter Stegen; Roberto, Pique, Lenglet, Alba; Rakitic, Busquets, Arthur; Messi, Suarez, Dembele
Leganes possible starting lineup:
Cuellar; Omeruo, Siovas, Tarin; Nyom, Gumbau, Vesga, Silva; Rodriguez, En-Nesyri, Braithwaite
Head To Head
Barcelona have won four of their five meetings with Leganes in La Liga, scoring in all five of those matches and netting 14 in total.
Leganes's solitary victory in that sequence came in the most recent meeting, however, thanks to those goals from El Zhar and Rodriguez in a little over a minute.
Los Pepineros have avoided defeat in two of their seven visits to Catalonia in the Spanish top flight, failing to score in four of those matches against Barca, Espanyol and Girona.
We say: Barcelona 2-0 Leganes
Leganes have what it takes to get the better of Barcelona, but the Catalans are a lot more consistent now compared to the opening quarter of the season, heading into this game on the back of a two-month unbeaten run in the league. Barca will be aware of their opponents' midweek win over Madrid, however, and they will certainly not take them lightly by fielding a weakened side.