"I want to apologise again," Mulumbu told the club's official website. "After it happened I knew it was a big mistake from me. But it's a good lesson for me and I need to move on now. I feel like I've let my teammates and the fans down. I hope I can bounce back and when I come back I need to be fit.
"Four weeks is really long so the best thing for me is to stay fit and focused because there are four games when I'm back and they are hard ones, including both Manchester clubs.
"I didn't want this break, but sometimes it's good. I will be fresh but I also have to keep working really hard with the coaches to stay fit. I need to give my best."
Mulumbu served his first game suspension last weekend when the Baggies stumbled to a 2-1 defeat at the hands of Arsenal.