After one season away, running back Blount returned to the Patriots on Thursday, having been released by NFL rivals Pittsburgh Steelers two days earlier.
Blount was let go by the Steelers for leaving the field early during Sunday's 27-24 win over the Tennessee Titans in Nashville.
Now back in New England, Belichick said Blount must work for his minutes for the American Football Conference (AFC) leaders.
"That will be up to him, just like everybody else," Belichick said on Friday.
"When he gets an opportunity, [it's] how much he can take advantage of it, how much he can be productive and what he can do with those opportunities [that] will determine how many more there are. It's totally up to him.
"We've talked about that. He knows that's the way it is, and he's excited about it."
Blount, who played 11 games for the Steelers this season and rushed 266 yards for two touchdowns, said he is looking forward to the challenge.
"Bill is a straight-forward shooter, he's a 100 percent honest person," the 27-year-old said.
"I truly believe that if I do what I have to do, then I'll make myself a role on this team. Whatever I have to do, I'm going to do it to be productive."
The Patriots host the Detroit Lions (7-3) at Gillette Stadium on Sunday.