Barcelona are set to complete the purchase of Marlon Santos from Fluminense before the end of the year, according to Sport. The Brazilian youngster is currently on loan at the Camp Nou but the Catalans are expected to activate an option to secure his services on a permanent basis amid the injury crisis in Luis Enrique's back-line.

The La Liga giants recruited the 21-year-old centre-back to strengthen the Barcelona second team during the summer transfer window, but with the hope he could eventually break into Luis Enrique's squad. The Brazilian spent pre-season training with the senior team and was included in the Champions League squad.

Barcelona confirmed on July that the loan agreement with Fluminense includes an option to secure his services permanently.

Reports in Spain suggest that Barcelona would need to pay around €6m (£5.4m, $6.5m) if they decide to activate the option at the end of the current campaign. The purchase would become mandatory for Barcelona should Marlon play five games for the first team during the current campaign.

Furthermore, that fee would increase if the Brazilian manages to establish himself with the La Liga giants, with Barcelona paying an additional €1m if he makes 20 first-team appearances and a further €1m at 40 appearances.

Marlon has excelled for the second team but is yet to make his debut under Luis Enrique.

However, Sport claims that the club have decided to activate the purchase option imminently because they will save up €2m should they complete his signing before he plays five first-team games.

The Spanish publications add that, despite the purchase option being set at €6m, Barcelona will only need to pay €2m because Fluminense still owe €4m from previous deals including Gerson and Kenedy, who is currently loaned out to Watford by Chelsea.

The Barcelona defence has been hit by injuries to key players such as Jordi Alba, Gerard Pique and Jeremy Mathieu in recent days, leaving Luis Enrique with just Javier Mascherano and Samuel Umtiti at centre-back. Luis Enrique is said to be seriously considering giving Marlon his first-team debut.

He has been training with Lionel Messi and co during the week and could be named in the squad for the coming games against Granada and Manchester City.