The midfielder sent the message via WhatsApp from his bed in hospital, a stone's throw away from the Parken Stadium, where five days earlier he had collapsed after suffering a cardiac arrest.
Denmark started fast and took the lead in the second minute through Yussuf Poulsen, with Eriksen watching on TV as the game was stopped in the 10th minute to pay tribute to the former Tottenham man.
Belgium hit back through Thorgan Hazard and Kevin De Bruyne to inflict a second defeat in two games on the Danes, who will qualify for the knockout stages with a victory over Russia as long as Finland lose against Belgium.
Eriksen, who will be fitted with a heart-starter, messaged his team-mates soon after the game, saying simply: "You were awesome." Denmark manager Kasper Hjulmand was equally proud. "The only thing I'm disappointed in is the result," he said.
"I didn't expect too much, but I can't describe the pride I feel for this squad, what they showed, the quality, days after almost losing their best friend. They totally dominated the best team in the world. It is amazing. I have so much respect.
"We were prepared for the emotional side of the game. I was very moved when the national anthem was on, but once we're together, we just push the 'on' button and we go."