Elche will be desperate for a win to distance themselves from the relegation zone, whilst Vallecano could find themselves in a European spot by the end of the weekend, should results go their way.
Since arriving in the summer, former Manchester United and Atletico Madrid striker Radamel Falcao has transformed Vallecano's fortunes, scoring three goals in his four La Liga appearances so far.
Coming off the bench to net in his first two Rayo matches, most impressively in the 96th minute to complete Vallecano's comeback victory over Athletic Bilbao, Falcao continued his strong scoring form on his first start for the club.
On the scoresheet in Rayo's 3-1 win over Cadiz, Falcao was less fortunate in their defeat to Osasuna, yet has still proved his worth to the club from the Madrid suburbs, despite many questioning if the 36-year-old could still cut it in the top leagues.
In their return to the first tier, Vallecano have enjoyed their best points return since the 1999-00 campaign, when they went on to end the season in ninth and Andoni Iraola's side will be targeting another top-half finish this time around.
Alongside Falcao's exploits, much of Vallecano's good fortunes this year can be attributed to their stellar home form, where Iraola's men have won all three of their matches at the Estadio de Vallecas.
They will be confident of making it a fourth when they take on Elche this weekend, yet with just one win from their last three home matches against Los Franjiverdes, another three points for Vallecano will not be considered a formality.
Despite this, Elche have won only one of their four away fixtures this season, whilst keeping just one clean sheet on their travels, making their visit North this weekend another potential headache for Fran Escriba.
Elche have actually managed to accumulate a decent defensive record this season, with only one other side in the bottom half having conceded fewer goals.
It has been in front of goal where Elche have struggled most, netting only five times during their eight La Liga matches – the second-worst record for any side in the division.
Scoring goals will be crucial for Elche if they are to survive this season and the form of Dario Benedetto could decide their fate, with the Marseille loanee already off the mark for his new side.
Benedetto will likely line up against Falcao in what is shaping up to be a battle of the talismanic strikers for Elche and Vallecano this weekend.
Elche's survival hopes may depend on how much they can keep their players fit, and Escriba will be conscious of not dropping too many points during a mini injury crisis for Los Franjiverdes.
That trio of Elche absentees are likely to return before the end of the month, whilst Jony Alamo is not believed to have been so lucky and will continue to sit out the coming fixtures.
Unlike their opponents on Sunday, Vallecano have near enough a full squad to pick from, with only Martin Merquelanz missing for Rayo this weekend.
The on-loan Real Sociedad winger has been absent since mid-September and with no return in sight, Merquelanz faces some more time in the treatment room before he takes to the pitch again.
Falcao started the previous two Rayo matches before the international break and is expected to lead the line for the unlikely European hopefuls on Sunday.
Rayo Vallecano possible starting lineup:
Dimitrievski; Balliu, Saveljich, Catena Marugan, F. Garcia; Palazon, Ciss, Comesana, A. Garcia; Trejo, Falcao
Elche possible starting lineup:
Casilla; Roco, Gonzalo, Barragan; Fernandez, Guti, Mascarell, Fidel, Mojica; Perez, Benedetto
We say: Rayo Vallecano 1-0 Elche
Having only won promotion from the second tier last season, Rayo's targets this season would have likely looked something similar to Elche's, yet focus has shifted away from a relegation battle, for now.
Vallecano can maintain their best start to a season in over 20 years with a victory over Elche, something that looks likely given the pair's form.