Real Madrid can step in and scupper
Sevilla's deal to sign former striker
Mariano.
The Lyon forward has been heavily linked with a move to Los Blancos this summer after netting 21 times for the Ligue 1 outfit last season.
Madrid have not yet made a move for their former star, who was only sold last year for €8m (£7.2m).
But Sevilla have now swooped in, agreeing a €30m (£27m) deal for Mariano, plus another €5m (£4.5m) based on the 24-year-old's performance at the Ramon Sanchez Pizjuan Stadium.
However, according to Marca, Madrid have first-option to sign the forward and now have 48 hours to let Lyon know whether they would like to open negotiations.
Julen Lopetegui's side may decide to allow Mariano to join their La Liga rivals due to a sell-on percentage included in his initial move to Lyon 12 months ago.
Madrid are set to take 35 per cent of any transfer fee Lyon receive for their star striker, meaning €12.5m (£11m) of Sevilla's €30m (£27m) bid would go into Lopetegui's transfer kitty.
Los Blancos may decide to re-sign Mariano after failing to replace Cristiano Ronaldo, who signed for Juventus last month.
Reports in Spain last week suggested Madrid had an agreement in place to sign former Liverpool ace Iago Aspas before Friday's transfer deadline.
However, news of the Celta Vigo star's move has gone cold over the weekend.
Speaking after losing the Spanish Super Cup final to Atletico Madrid, Lopetegui rejected claims his side needed extra recruits brought in before the end of August.
“What was outlined by the club's sports policy does not change by this final," he told reporters.
“Now La Liga starts, which is a very important title for me, and we have to start well.”
Madrid have won their opening two games of the La Liga season, with Gareth Bale filling the shoes left vacant by Ronaldo.
The Spanish giants have until 11.59pm on Friday evening to complete any transfer deals.