Arsenal are set to lose captain Thomas Vermaelen after it was widely reported that the defender had agreed a deal in principle to join Manchester United. 

British newspaper The Telegraph reports that United will have to agree a fee but with Vermaelen having just one year left on his contract, the Gunners may be forced to sell rather than risk losing him for free.

Vermaelen struggled to force his way into the first team last season thanks to the superb partnership formed between Laurent Kocielny and Per Mertesacker.

The Belgian has also had a number of injuries that have hampered his opportunities in the first team, despite initially impressing after joining from Ajax and becoming the club captain.

It is believed that new Manchester United boss Louis van Gaal is keen to strengthen his backline after Nemanja Vidic departed for Inter Milan, and Rio Ferdinand was not handed a new deal at Old Trafford.

Vermaelen is currently in Brazil with the Belgium squad but it is believed that he wants his future to be sorted out before the World Cup ends.

The 28-year-old has the same agent as Robin van Persie who was key to helping the Dutch striker secure a move from Arsenal to Manchester United.

Should Vermaelen depart then it would be another major blow for Arsenal supporters who have seen Bacary Sagna join Manchester City and former captain Cesc Fabregas move to Chelsea.