Paris St-Germain star Neymar played only six minutes as Brazil edged out African champions Cameroon on Tuesday.
Neymar suffered an adductor muscle injury while taking a shot and was replaced by Richarlison.
The Everton forward proved to be the match-winner, powering home a header on the stroke of half-time.
Manchester City's Gabriel Jesus struck the post for Brazil in the second half, while Arthur hit the crossbar with a long-range effort.
The 29,669 fans at Stadium MK cheered loudly when Neymar came out to warm-up, but were equally displeased when he hobbled off.
Brazil team doctor Rodrigo Lasmar said: "He felt discomfort. He will need a bit more time to evaluate it and take a scan, but in principle it is not a serious injury."
The former Barcelona superstar received support from his PSG team mate Eric-Maxim Choupo-Moting.
"He wanted to play," the Cameroon forward said.
"I hope for him it's not that serious, but you have to be careful and if you feel something there, then you should not risk anything."
Cameroon were using the game as continued preparation for their defence of the African continental title when they host the Africa Cup of Nations next year.
"I'm very proud of the team," Indomitable Lions coach Clarence Seedorf said after the game.
"It was not an easy task four days after we had a hard match against Morocco as well. This gives a lot of confidence for the future."
There were a number of other friendlies on Tuesday. Morocco beat neighbours Tunisia 1-0 away from home, Nigeria drew 0-0 with Uganda, and South Africa scored deep in stoppage time at the end of the game to equalise in a 1-1 draw with Paraguay,