The Frenchman flew to London after New York Red Bulls' game against Real Salt Lake to spend an hour with his former Arsenal teammate after the Bolton midfielder's cardiac arrest.
Henry traveled over 3,500 miles from New York to spend time with his former Gunners teammate and his family at the London Chest Hospital.
The New York Red Bulls forward also revealed that Muamba is able to "talk perfectly" as he continues to recover after collapsing against Tottenham at White Hart Lane on Saturday.
The Frenchman announced on his Twitter feed: "Leaving back to America - Fabrice is getting a lot better which is fantastic. I will let you know more when I'm back in the US.
"Fabrice is in a stable condition and can talk perfectly."
One of Muamba's doctors had earlier revealed that the former England under-21 international had stopped breathing for 78 minutes before finally being revived in hospital.
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