Lanzini underwent surgery on his knee, but is now back at the club to continue his rehabilitation.
While he will not be available to play anytime soon, his presence with the rest of the squad could help lift spirits at the club.
Richard Collinge, West Ham's head of medical, told the club's official website: "We're really pleased for Manu and it's great to have him back.
"He's now at the three-month stage, so I flew out to see Manu and his consultant Dr Cugat at the weekend and the doctor is very happy with his progress after three months.
"Rehab-wise, we have a plan in place and Manu is very disciplined and very motivated and we're moving in the right direction."