Only Salih Özcan has left Borussia Dortmund's central midfield so far this summer, and the 28-year-old barely featured for the club anyway, but reinforcements could still be needed there should Felix Nmecha or Marcel Sabitzer depart before the window closes.
According to Mundo Deportivo, Borussia Dortmund are seriously exploring a move for the 19-year-old Marqués, whose path to regular football at Barcelona has narrowed considerably under Hansi Flick given the competition for places, a situation set to worsen further with Rodri's expected arrival at the club as part of a wider midfield reshuffle at the Camp Nou that is also set to see Marc Casadó sold this summer.
Marqués, who has been labelled by some in Catalonia as a potential heir to Frenkie de Jong's role in midfield, made his senior debut for Barcelona in a 3-0 win over Mallorca last season and went on to be included in 11 further league squads, collecting a small handful of minutes along the way, including in the club's title-clinching campaign.
That limited game time has convinced him a move away is the right next step, with Sporting Braga currently understood to be in pole position for his signature, driven by head coach Carlos Vicens, who previously worked in Manchester City's academy and has a track record of trusting young players with regular minutes.
Manchester City are also working on a deal of their own, with the Premier League champions planning to sign the Spaniard before loaning him straight to sister club Girona for regular game time in Spain's second tier.
Dortmund's chances are said to be boosted by the good relationship between the two clubs, strengthened by Karim Adeyemi's move to Barcelona earlier in the window on a contract running until 2031.
Barcelona are willing to sell Marqués permanently, but only on the condition that any deal includes a buy-back clause and a percentage of any future sale, allowing the Catalan club to retain the option of bringing him back in future should he develop as hoped elsewhere, mirroring the structure used in several of the club's recent academy exits.