The Brazilian star played only 26 minutes as a substitute in the second half before leaving the field with a suspected right hamstring strain during Monday's 3-0 victory over Esteghlal in the AFC Champions League Elite.
The 32-year-old, who transferred from Paris Saint-Germain in a high-profile deal in 2023, had been out of action for over a year following surgery on his right knee until his return last month.
“Neymar, it’s not an easy case,” said Al Hilal’s Portuguese coach Jorge Jesus.
“On the medical level, his knee is healed, but then he will have problems like today, muscle problems because he hasn’t played for a long time.
“Now he has a muscle injury. I don’t know how long he won’t be able to train, two weeks at least,” he added.
Al Hilal, the current champions of Saudi Arabia, have not included Neymar in their roster for the ongoing Saudi Pro League season that commenced last month.
However, the former Barcelona star, who is said to earn approximately 100 million euros ($112 million) annually, is set to participate in the AFC Champions League Elite, the premier club competition in Asia.
“It felt like a cramp, but very strong!” he wrote on Instagram. “I’ll do some tests and hope it’s nothing more serious.
“It’s normal for this to happen after one year, the doctors already warned me, so I have to take care and play more minutes.”