The Tottenham playmaker was among those seen praying on Saturday evening as medics rushed onto the pitch to tend to Muamba.
The Bolton midfielder is currently being cared for at the London Chest Hospital after suffering a cardiac arrest, with his condition stable but still critical.
Van der Vaart has spoken for the first time about the events which unfolded around him during the abandoned FA Cup quarter-final clash, and the Dutchman is still coming to terms with what happened.
He told Spurs' official website: "It's almost incomprehensible what has happened.
"(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.
"I'd like to express my sincere support to the family, team-mates and everyone who is involved with Bolton Wanderers.
"Fabrice, we'll keep praying for you and I hope with all my heart that everything will be all right again."