"Honestly, I do not know. I think talking now is bad because of the heat of the moment. Maybe I'm not thinking straight," an emotional Neymar told reporters in Al Rayyan, Qatar.
"To say that this is the end would be rushing myself, but I don't guarantee anything either. Let's see what happens going forward.
"I want to take this time to think about it, think about what I want for myself. I will not close the door to playing with Brazil, nor do I say 100% that I'll come back."
Neymar scored late in the first half of extra time to give Brazil the lead, but Croatia equalised when Bruno Petkovic scored in the 117th.
Croatia goalkeeper Dominik Livakovic saved a penalty attempt by Rodrygo, and Marquinhos later hit the post.
Neymar didn't take a penalty in the shootout because he was assigned as the fifth and last taker, but Marquinhos' miss sent Croatia to the World Cup quarterfinal after only four tries.
"He should have taken the fifth and decisive penalty. The player with the most quality and mental skills is the one to be in charge in the moment when the pressure is high," Brazil coach Tite said.
Brazil great Pele remained in a hospital in Brazil treating a respiratory infection that was aggravated by COVID-19. The latest medical report indicated that the 82-year-old Pele was doing OK.
Neymar joined Ronaldo (Nazario) as the only Brazilian men to score multiple goals at three different World Cups.
The 30-year-old Neymar scored his 77 goals in 124 matches for Brazil. Pele's goals came in 92 appearances with the national team between 1957 and 1971.
The Paris Saint-Germain forward began the World Cup two goals behind Pele. Neymar now has 77 goals in 124 international appearances.
Brazil women's forward Marta holds the country's all-time record with 115 goals in 171 games.
He guided them to the Confederations Cup title in 2013 but suffered World Cup heartbreak the following year when he was injured in Brazil's quarterfinal win against Colombia and was unable to play in the country's humiliating 7-1 semifinal defeat to Germany on home soil.
Neymar was also a key part of the Brazil side that reached the quarterfinals of the tournament four years ago in Russia, where they were beaten by Belgium. He missed out on Brazil's 2019 Copa America triumph through injury and was on the losing side in last year's final against Argentina.
The 30-year-old has enjoyed a glittering club career, with honours including two LaLiga titles, a Champions League trophy, four Ligue 1 titles and a Copa Libertadores.
Information from Reuters was used in this report.