The Paris Saint-Germain star has been sidelined since February after needing surgery on a fractured foot.
After Brazil named their 23-man squad on Monday, team doctor Rodrigo Lasmar revealed Neymar was progressing well and could potentially face Croatia at Anfield on June 3.
"We've been making new exams on Neymar and his evolution is really fine," he told a news conference.
"Next week, he'll be able to start training with the group. It's progressive work and next week our idea is that he starts to work with the ball and the goal is that he can be fully fit to work with [coach] Tite in his final phase, so that he can take part in the first friendly.
"I'm giving these details to you a little bit before Tite, but only to tell you that he'll be working to get back all conditions and of playing with the group."
As well as their friendly against Croatia, Brazil will face Austria on June 10 before their World Cup opener against Switzerland a week later.
Tite hopes Neymar can return to his best, but the coach accepted the 26-year-old would face several challenges.
"A high-level athlete trains at the highest possible intensity and level," he said.
"The only difference he has to manage is the psychological pressure because he doesn't have the press, public now, all this stuff.
"All the rest is the same to everybody. And the technical staff works like this, in its highest level.
"So, Neymar will have all this work to get back to his normal level."