Neymar, who was not part of Brazil's squad that won the Copa America on home soil in 2019 thanks to injury, wrote on social media: "Losing hurts me, it hurts me... it's something I haven't learned to live with yet. When I lost, I went to give a hug to the biggest and best in history that I saw playing.
"My friend and brother MESSI, I was sad and I told him: 'You beat me.' I'm very sad for having lost. But this guy is awesome! I have great respect for what he has done for football and especially for me. I HATE TO LOSE!!!! But enjoy your title, football was waiting for you for that moment! CONGRATULATIONS BROTHER."
It was Argentina's first major title in 28 years and allowed Messi to win his first international competition after four defeats in major finals.
Messi, a six-time Ballon d'Or winner, was voted the player of the tournament after his four goals and five assists in the competition.
The Argentina squad got a hero's welcome as they arrived in Buenos Aires from Rio de Janeiro on Sunday evening.
An elated Messi thanked "God for being Argentinian" and remembered the late Diego Maradona in an emotional message he posted on Instagram.
Messi wrote: "At the Maracana and in a clasico against Brazil...I cannot be any prouder to captain this spectacular group. I dedicate this success to my family that always gave me strength to carry on, to my friends that I love so much, to all the people that support us, especially to the 45 million Argentinians that have had such a bad time with this s--- virus, above all to those that affected them closely.
"It's for all of you. And of course, also to Diego [Maradona], who for sure supported us wherever he is. Thank you God for all you gave me and thanks for making me Argentinian!!!"