The English club will open their new season away to Arsenal on August 17, while Rayo's La Liga campaign will begin against Real Sociedad on August 18.
Match preview
Wolves played three times during their US Tour, beating West Ham United 3-1 in their opening pre-season fixture, before suffering a 3-1 defeat to Crystal Palace in their second friendly.
Gary O'Neil's side were last in action on August 3, recording a 3-0 victory over RB Leipzig, with the team concluding their tour of the United States in impressive fashion.
Wolves will now round off their preparations for the new campaign with a clash against Rayo on Saturday afternoon, before starting their new Premier League season away to Arsenal on August 17.
O'Neil's team will also face Chelsea and Nottingham Forest in the Premier League in August, and Wolves will be aiming to improve on last season's 14th-placed finish in England's top flight.
Wolves have made four signings this summer, with the most expensive of those proving to be Rodrigo Gomes, who has arrived from Braga, while Pedro Lima, Tommy Doyle and Jorgen Strand Larsen have also joined.
Rayo, meanwhile, finished 17th in La Liga last season, five points above the bottom three, so the capital outfit are preparing for another campaign in Spain's top flight.
Los Franjirrojos have made four signings this summer, bringing in Pedro Diaz, Pelayo Fernandez, Gerard Gumbau and Adrian Embarba to boost their squad for the new campaign.
Inigo Perez's side have played five friendlies this summer, opening their preparations for the new campaign with a 2-2 draw against Braga, before losing four straight games to Vitoria Guimaraes, Heerenveen, Cordoba and Bournemouth.
Rayo will conclude their preparations for the new campaign against Wolves on Saturday afternoon, before opening their La Liga season away to Real Sociedad on August 18.
The capital side will play four league games before the end of August, following the clash with Real Sociedad with matches against Getafe, Barcelona and Espanyol.
Wolverhampton Wanderers friendly form:
W
L
W
Rayo Vallecano friendly form:
D
L
L
D
L
Team News
Wolves head coach O'Neil is set to name a familiar XI on Saturday afternoon, with new signing Larsen likely to lead the line with support from Pablo Sarabia, Gomes and Hwang Hee-chan.
Mario Lemina should operate alongside Doyle in midfield, while Jose Sa is set to start between the sticks, having featured off the bench against Leipzig last time out.
Pedro Neto featured for the final 20 minutes of the friendly with Leipzig and should again make an appearance off the bench, while Nelson Semedo is set to continue at right-back.
As for Rayo, it is expected to be a familiar XI from last season, with Sergio Camello likely to lead the line from the first whistle, while Alvaro Garcia and Randy Nteka could also start.
Gumbau is a new signing in central midfield and should be in the XI, with Oscar Valentin and Pathe Ciss also expected to be included in that area of the field.
There will be changes throughout the contest, but head coach Perez will be thinking about the new campaign, so key players are likely to receive more minutes in the friendly fixture.
Wolverhampton Wanderers possible starting lineup:
Sa; Semedo, Mosquera, Toti, Ait-Nouri; Lemina, Doyle; Sarabia, R Gomes, Hee-chan; Larsen
Rayo Vallecano possible starting lineup:
Cardenas; Ratiu, Lejeune, Mumin, Espino; Valentin, Gumbau, Ciss; Nteka, Camello, A Garcia
We say: Wolverhampton Wanderers 3-1 Rayo Vallecano
Wolves were excellent against Leipzig last time out and will be in a confident mood ahead of their clash with Rayo. The La Liga team will provide competitive opposition, but we are expecting Wolves to conclude their preparations for the new campaign with a victory.