Celta Vigo boss Abel Resino has said there is plenty of suspicion - but no real proof - that end of season matches in La Liga are often fixed.
Rumours about results being arranged in advance and third-party payments - known as maletines, or little suitcases - are a staple of Spanish springtimes.
Levante's players have said they will help with any investigation, while new Liga de Futbol Profesional president Javier Tebas has vowed to root out what he described as the "cancer" of match-fixing in La Liga.
This week, Deportivo fans unfurled a banner at training that accused Real Zaragoza of saving themselves "year after year" with a maletin.
And in a move described as "third-party mussels" by Marca, a Celta supporters' group is offering a kilo of shellfish to Espanyol and Athletic players if they can do Los Celestes a favour in their games against Deportivo and Zaragoza this weekend.
Resino said: "They tell me that one game from the next round is already bought. But is there anyone who can show it?
"What I believe is that everyone sends up a trial balloon to try and take advantage of the situation. If the LFP are paying attention, then perfect. From there, they must show there are irregularities and take the appropriate measures."
Resino suggested that few in Spanish football were really interested in a thorough investigation. "Does anyone really believe that, in Spain, they are going to pull off the blanket, as was done before in Italy or other countries?" he asked. "It looks unlikely and difficult to me."
Celta, currently 19th in the table and three points from safety, have no game this weekend because their match against Atletico Madrid was brought forward due to Atletico's Copa del Rey final appearance.
Resino said it was likely his side would have to win their two remaining matches to have any chance of survival.
"We must win the games we have left against Valladolid and Espanyol," he said. "I hope that Deportivo and Zaragoza at least do not win this weekend. If they both lose, even better. That would help our chances of salvation."