Rock-bottom Betis are on a seven-game winless run in the league and the 4-0 weekend defeat to city rivals Sevilla heaped further pressure on the head coach.
But Mel received the backing of director Rafael Gordillo on Wednesday and knows that victory over fellow strugglers Vallecano would lift his men, who are three points from safety, of the foot of the table.
Barcelona are enjoying entirely different fortunes at the top end of the division, with Gerardo Martino's men having dropped just two points in 14 league games.
Up next for the defending champions is a trip to Athletic Bilbao, who have not lost a home league game this season and sit fifth.
Waiting to pounce on any slip-up from the league leaders are Atletico Madrid and Real Madrid.
Both are in action on Saturday, as Atletico head to mid-table Elche, while Carlo Ancelotti's side welcome struggling Real Valladolid.
Leading scorer Cristiano Ronaldo is a doubt as he continues to struggle with a hamstring injury that ruled him out of Wednesday's UEFA Champions League clash against Galatasaray.
Elsewhere on Saturday, Celta Vigo, out of the relegation zone on goal difference only, will look to avoid a third consecutive defeat when they take on an Almeria side who are level with them on 12 points.
Espanyol, fresh from a 4-1 victory over Vallecano, will need to be at their best to keep Real Sociedad striker Carlos Vela quiet after he scored all four of his side's goals in the 4-3 triumph over Celta last time out.
The weekend's action begins with two games on Friday, with a chastened Getafe side aiming to provide a response to their 7-0 loss against Atletico Madrid when they play host to Levante.
And fourth-placed Villarreal, winless in their last two home games, meet Malaga at El Madrigal.
The final two matches in round 15 see Granada host Sevilla, and Valencia tackle Osasuna.
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