Valladolid have lost three in a row but are four points clear of the dropzone, while Betis are two points and two places better off in 14th.
Betis have already switched focus to next season following the recent appointment of experienced head coach Manuel Pellegrini, who will officially take over next month.
Pellegrini has targeted European football with Los Verdiblancos, having previously guided Malaga and Villarreal to the latter stages of the Champions League.
The 66-year-old will have his work cut out if this season is anything to go by, though, with 13th place now the best Betis can hope for.
Two wins in seven matches since sacking Rubi is not the best return, although Betis have at least avoided being dragged into a relegation battle.
That was not the case 10 games in when a 1-0 loss to Granada left them in the bottom three. It has been catch up ever since and Rubi was ultimately unable to save his job.
Betis may be on a disappointing run but Valladolid enter this final-day fixture in even worse form, losing each of their last three matches.
The White and Violets went down 3-1 to Eibar last time out and face losing four on the spin for the first time since March 2019.
Relegation is out of the equation, though, as they hold a four-point buffer on Leganes in 18th place.
Valladolid are winless in their last six La Liga home games against Betis, failing to score in five of them in a run stretching back to January 2003.
However, Betis have not picked up maximum points on their travels in 11 games, with Mallorca the only side in the division with a worse away record.
Real Valladolid's La Liga form: DDWLLL
Real Betis' La Liga form: LLDWLL
Elsewhere, Marc Bartra was an unused substitute last time out and will be eager for a recall for this final match of the season.
Real Valladolid possible starting lineup:
Caro; Moyano, Olivas, Sanchez, Nacho; Hervias, Alcaraz, Emeterio, Villa; Ramirez, Unal
Real Betis possible starting lineup:
Martin; Emerson, Bartra, Sidnei, Pedraza; Gonzalez, Carvalho; Canales, Fekir, Joaquin; Moron
We say: Real Valladolid 1-1 Real Betis
Valladolid may not have the best of home records this term, winning just four times at the Estadio Jose Zorrilla, but Betis have somehow been even worse when it comes to picking up away points - just 10 from 18 matches. This may well be a classic case of two out-of-form sides cancelling each other out on the final day.