The star-striker has not featured at all this season after injuring his ankle on international duty with England last August.
West Ham's Head Physiotherapist Steve Allen confirmed, "Dean underwent a successful diagnostic arthroscopy operation on his left ankle to remove a significant amount of scar tissue - a problem directly linked to the original injury he sustained.
"We have left no stone unturned in our attempt to get Dean back out on the football field as soon as possible, but it was clear that he had gone as far as he could with the methods that had been used, and the only option was to have another look at the injury site.
"We sought the opinions of the leading ankle specialists in the country and, following their advice, the decision was made to operate.
"It will be six weeks before he is back running, and we felt that the timing was right, in order for Dean to make a fresh start with the rest of his team-mates when the squad returns for pre-season training in the summer. We look forward to seeing him back to full fitness then."