Manchester United will ramp up their efforts to sign Arsenal defender Thomas Vermaelen for as much as £15m in order to beat Barcelona to the signature of the Belgian defender, according to reports.

Vermaelen rejected the chance to extend his contract at the Emirates, and with United’s central defence the main area for concern heading into the new season, Louis van Gaal is expected to re-launch the move that was halted by Arsene Wenger earlier this summer.

As well as Vermaelen, Ajax wing-back Daley Blind is also on Van Gaal’s wish list, with the former Netherlands manager looking to bring in players that will fit into his plans to play a 3-5-2 formation that puts the emphasis on the two wide players to shift from defence to attack.

Arsenal are reluctant to sell Vermaelen to a Premier League rival and would much rather see him move to Spain with the Catalan club. A move to United would also see them lose another player to Manchester, with no less than six first team players moving north in recent years. Emmanuel Adebayor, Gael Clichy, Samir Nasri, Kolo Toure and most recently Bacary Sagna have all joined Manchester City since 2009, while ex-Gunners captain Robin van Persie moved to the red half of the city in 2012.

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Getty Images Manchester United: Potential summer transfer targets Xherdan Shaqiri Bayern Munich winger Xherdan Shaqiri has struggled to force his way into the first team at the Allianz Arena and could be a target for United as well as rivals Liverpool. His impressive displays for Switzerland this summer could make it harder to prise him away. GETTY IMAGES Manchester United: Potential summer transfer targets Alex Song Barcelona are understood to be ready to let the former Arsenal player leave this summer. Could provide some strength to United's midfield. Could also bring embarrassment judging by his behaviour at the World Cup. GETTY IMAGES Manchester United: Potential summer transfer targets Fabio Coentrao Supposedly came within hours of signing in January, the Portuguese left back could be brought in to provide back-up to Luke Shaw. Manchester United: Potential summer transfer targets Julian Draxler A long time Arsenal target, United are reportedly interested in pinching the young German with a bumper offer. Seems unlikely though. Arsenal also strongly interested. Manchester United: Potential summer transfer targets Sami Khedira The Germany international is reportedly being pursued by a host of sides, and United might be wise to get in the mix as they look to add some quality to a fairly feeble looking midfield. Real Madrid appear open to letting him go with the 27-year-old having just one year left on his contract. Arsenal and Chelsea are among the others keen on signing the World Cup winner. Manchester United: Potential summer transfer targets Edinson Cavani The Uruguayan hitman would prove pricey and tricky to snatch away from PSG and it seems unlikely United have enough to offer him. 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Despite remaining as Arsenal’s club captain last season, Vermaelen made just seven appearances as Per Mertesacker and Laurent Koscielny formed a strong partnership to keep Vermaelen out of the starting line-up.

Van Gaal hopes that signing Vermaelen and Blind would give them the necessary strength at centre-back, as well as provide cover for new summer signing Luke Shaw at left-back after both Patrice Evra and Alexander Buttner left the club this year.

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Barcelona are believed to have lodged a £10m bid for Vermaelen, and although the reigning FA Cup champions would like to make for from Vermaelen’s departure, they could accept a low offer in order to keep him out of the clutches of United – who could be forced to pay up to £5m more than the Catalans.

The defence is certainly an area of concern for Van Gaal, having seen veterans Nemanja Vidic and Rio Ferdinand depart in the biggest summer of change for some time. Van Gaal’s preferred back-three during their pre-season tour of the United States has been the combination of England defenders Phil Jones and Chris Smalling along with Northern Ireland international Jonny Evans.

However, the former pair are yet to make their mark at Old Trafford, and while they could use the opportunity to cement a place in the United line-up, Van Gaal is still keen to add reinforcements to strengthen his effort to take United back to the top-four and mount an unlikely Premier League title challenge.

United returned home from the US this week and a number of them are set to learn whether they feature in Van Gaal’s plans later this week when the players return to training on Friday. Reports suggest that three players will definitely be put up for sale, although as many as six could yet leave Old Trafford as the rebuilding process since Sir Alex Ferguson’s retirement moves up another gear.