The former Juventus striker signed for the Baggies last week.
"Nicolas seems a really lovely lad," Foster told the Albion website.
"After the first session you could see little glimpses of what he has got. He's going to be a fantastic addition to the squad. I'm sure everyone will welcome him.
"We're all looking forward to seeing him in action. I really want to see his butterfly celebration too.
"I always remember seeing him do that when he scored goals at Chelsea. It's an awesome celebration.
"I want to see him do it plenty of times this season!"