Neymar started Brazil's 3-0 win over Ghana on Friday, where Spurs star Richarlison scored twice and Marquinhos was also on target.
Neymar registered two assists in the victory but the main talking point surrounding him came in the mixed zone afterwards.
The former Barcelona superstar fielded questions from journalists but when it came to Mbappe, Neymar didn't fancy answering.
He was asked about his relationship with Mbappe, at first replying, "I don't understand" in English.
Neymar then said, "With Kylian?" before sighing and adding, "I don't" - walking away from the media and not elaborating any further.
The lack of comment from Neymar will only intensify rumours that all is not well between two of PSG's main stars.
There were reports of a rift between the two players over a penalty in the 5-2 win over Montpellier last month, with Neymar refusing to let Mbappe take a second spot-kick.
Neymar appeared to like a number of anti-Mbappe social media posts after their alteration and it was claimed that Sergio Ramos intervened in the dressing room.
The duo looked like they had patched things up and combined well on the pitch for Christophe Galtier's side, though Neymar did fume at Mbappe for being selfish against Juventus.
Mbappe addressed the dynamic between himself and Neymar last month, admitting that they don't always see eye-to-eye.
"To talk about Neymar, this is the sixth year, I think we've always had a relationship like this based on respect," he said in a press conference.
“But we've always had moments like this where sometimes we've had moments that were a bit colder and moments that were a bit hotter.
"There are times, you'll see, when we're the best of friends and sometimes we don't talk so much, it's the nature of our relationship that's like that.”
Mbappe was on the scoresheet for France against Austria on Thursday and said he has "more freedom" when playing with the national team than for his club.
However, he has courted controversy after refusing to take part in a photoshoot over his image rights.
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