The England striker explained to Goals on Sunday that he is damaged a small ligament behind his knee and that it will take at least another few weeks before he is fully fit.
“I have done my PCL," he said.
"It's a ligament behind your knee and they say you don't really need it if your muscles are strong. It protects it, but I have done a little damage to it, it's not torn fully.
"I have to build up the muscles and do some rigorous rehab work to protect the knee and it is going to be like that for the rest of my career.
"Hopefully I will be back some time in January. I just need to get back fit and help the Hammers.
"It was welcoming news when I got told by the specialist and hopefully I can focus on getting back fit and scoring goals."