Real Madrid could swoop in to bring Mariano back to the Santiago Bernabeu, despite Sevilla's negotiations with Lyon being at an advanced stage.
Mariano joined Lyon from Real last summer for €8m and enjoyed an excellent debut season in Ligue 1, scoring 21 goals in 45 appearances for the French side.
Sevilla now want to bring Mariano back to Spain and have reportedly struck an agreement with Lyon, but a clause in the contract that the Dominican international signed last summer allows Real Madrid first refusal on any agreed deal.
Marca reports that Real now have the option to torpedo Sevilla's move and bring Mariano back to the Spanish capital, or stand aside and pocket 35% of his sell-on price.
Lyon president Jean-Michel Aulas told Real earlier this summer that he planned to sell Mariano to a Premier League club for around €70m, but he was unable to find a club who were willing to pay that fee.
Sevilla's bid for Mariano is €30m up front, with an additional €5m in bonuses. Real Madrid would pocket €12m of that, so now they must decide whether to hijack the deal or not.
Mariano was prolific for Real Madrid Castilla in 2015/16, scoring 27 goals in 33 games for the European champions' reserve side.
He fared quite well for the first team as well, scoring five goals in 14 appearances during his breakthrough season, but this was not deemed impressive enough for him to be kept on.