Neymar described the injury that has put his World Cup on ice as "one of the hardest moments of my career" after the Brazil star was sidelined by an ankle problem.
He has been ruled out of the Selecao's second Group G game against Switzerland on Monday and could also miss the tussle with Cameroon four days later.
The Paris Saint-Germain forward suffered a heavy knock to his right ankle after a challenge from Nikola Milenkovic in Thursday's 2-0 win against Serbia, needing to be substituted in the 80th minute.
He was fouled nine times in the game, more than any other player in a World Cup matchday one group game in Qatar. The next highest number was the five sustained by Spain's Gavi against Costa Rica.
Neymar is looking to crown his fine career with a World Cup triumph, and he is confident about getting back to full fitness and playing a role later in the tournament.
"The pride and love I feel for wearing the shirt has no explanation," he wrote on Instagram. "If God gave me the opportunity to choose a country to be born, it would be BRAZIL.
"Nothing in my life was given or easy. I always had to chase my dreams and my goals. Never wishing evil on anyone but helping those in need.
"Today has become one of the hardest moments in my career... and again in a World Cup. I have an injury yes, it's annoying, it's going to hurt but I'm sure I'll have the chance to come back because I will do my best to help my country, my team-mates and myself."
He was seen in tears on the Brazil bench towards the end of the game, and it would be a grim state of affairs for the 30-year-old if his injury is not one he quickly shakes off.
Neymar added: "Wait a long time for the enemy to knock me down like this? NEVER! I am a CHILD OF THE IMPOSSIBLE GOD and my FAITH is endless."
Fitness worries at the World Cup are nothing new for Neymar. He was forced out of the 2014 finals, which Brazil hosted, when he suffered a back injury in the quarter-final win against Colombia.
Across the 2014 and 2018 World Cups combined, Neymar was fouled a leading 44 times – or once every 21 minutes, more often than any other player impeded on at least 25 occasions.