Andy Carroll’s future at West Ham has been thrown into serious doubt after the club attempted to sell the England striker to China behind his back, it has been revealed.

The Times reports that West Ham wrote to Mark Curtis, the former agent of Carroll, giving him “exclusive authority” to structure a move for the forward to either Tianjin Quanjian, Hebei China Fortune or Shandong Luneng Taishan.

It emerged during the January transfer window that West Ham had rejected three offers for Carroll, with interest from China persisting given that their deadline day did not come until Tuesday 28 February.

But it has now been reported that West Ham gave permission for Curtis to try and sell 28-year-old Carroll on their behalf, with a letter sent by Andrew Pincher, the club’s secretary, on 15 February confirming an agreement following a meeting with West Ham co-owner David Sullivan.

The letter, seen by The Times, read: “Following your meeting with David Sullivan [the West Ham co-owner], I write to confirm you have the exclusive authority of the board of directors to represent West Ham in discussions with football clubs in China in order to explore interest and options for the potential sale and permanent transfer of the registration of Andy Carroll during their first and current transfer window. This exclusive authority shall expire on March 1, 2017.”

However, it adds that West Ham would have agreed to a deal only if they had a replacement in place, which raises questions over whether a move would have been immediate or if it was in advance of a summer move.

Asked this week about the agreement, Curtis said: “As far as I am aware, West Ham are not interested in selling Andy.”

Carroll is hoping to return for West Ham against Chelsea on Monday (Getty)