Espanyol are currently 10 points behind 17th position, while Leganes are nine points from safety, with both clubs facing the real possibility of dropping into the Segunda Division.
Espanyol have not mathematically been relegated, but it is going to take some turnaround from the Catalan outfit in their final five matches to secure their status at this level of football.
Indeed, a record of five wins, nine draws and 19 defeats from their 33 matches has left them rock bottom of the table, some 10 points behind 17th-placed Celta Vigo on the same number of games.
Los Periquitos have not played outside of Spain's top flight since the 1993-94 campaign, while they actually finished seventh in La Liga last season, picking up 14 wins from their 38 matches.
Now under the management of Francisco Rufete on an interim basis, Espanyol have lost each of their last four in the league, including a 2-1 defeat away to Real Sociedad on Thursday night.
Leganes, meanwhile, are also in serious trouble of being relegated, sitting just one point and one position above Espanyol ahead of kickoff on Sunday afternoon.
Javier Aguirre's side have not picked up a win since returning to action after the lockdown period, losing four of their six matches, including their last two against Osasuna and Sevilla.
Los Pepineros are competing in their fourth season at this level of football, but they only just survived in both 2016-17 and 2017-18, finishing 17th, before claiming 13th last term.
A victory this weekend would certainly give them a chance of escaping the relegation zone, but they have only managed one away win in La Liga this term, losing nine of their 16 matches.
Espanyol La Liga form: WDLLLL
Leganes La Liga form: LLDDLL
As for Leganes, Spanish midfielder Roque Mesa is suspended due to the yellow card that he picked up against Sevilla, while Kenneth Omeruo, Oscar Rodriguez, Guido Carrillo and Alexander Szymanowski are injury doubts.
Espanyol possible starting lineup:
Diego Lopez; Gomez, Espinosa, Cabrera, Vila; David Lopez, Roca; Embarba, Melendo; De Tomas, Wu Lei
Leganes possible starting lineup:
Cuellar; Rosales, Bustinza, Awaziem, Silva; Amadou, Recio, Perez; Gil, Guerrero, Aviles
We say: Espanyol 2-1 Leganes
There is simply no downplaying the importance of this match for both sides; a draw suits neither and therefore it would not be a surprise to see an open game. Espanyol have the worst home record in the league this season, but we fancy the Catalan side to pick up all three points courtesy of a narrow win.