The Dutch midfielder has described his horror at seeing the Bolton player suffer a cardiac arrest during the sides' abandoned FA Cup quarter-final clash on Saturday
The Dutch playmaker was seen praying on the pitch as paramedics rushed to Muamba's aid and he has described witnessing the incident as a harrowing experience.
"It's almost incomprehensible what has happened," he told the club's official website.
"[It was] simply horrifying to see such a young player on the ground struggling for his life.
"I was standing about 10 metres from him but I didn't see him fall. It happened behind my back, but when I turned I immediately knew things weren't good.
"At that time all players on the field felt the panic as well. It was horrible to witness, it's the absolute low in my football career."
The 29-year-old also wished to convey his sympathies to the player concerned, his family and Muamba's team-mates.
"I'd like to express my sincere support to the family, team-mates and everyone who is involved with Bolton Wanderers," he added.
"Fabrice, we'll keep praying for you and I hope with all my heart that everything will be all right again."