Vincent Janssen lost 20 minutes of his memory after a heavy collision with Simon Mignolet in Netherlands' 1-1 friendly draw against Belgium.
Davy Klaassen gave Danny Blind's team a 38th-minute lead from the penalty spot in Amsterdam, by which time Stijn Schaars and Janssen had already been forced out of the action.
Jeremain Lens suffered a pulled hamstring before Yannick Carrasco hit a deflected equaliser eight minutes from time, but it was the injury to Tottenham striker Janssen that caused the most concern to Blind ahead of Sunday's World Cup qualifier against Luxembourg.
"Vincent Janssen is going to be a very difficult story," he told reporters.
"The physician told me it is a concussion. He lost 20 minutes of his memory, and doesn't know what happened.
"We have to be careful with that and talk it through."
Wesley Sneijder captained Netherlands on his 125th international appearance, leaving him second only to Edwin van der Sar's 130 on the all-time list.
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"Until we conceded a goal, we didn't give away chances," he said. "The organisation was good, but lacked in creativity."
"We should be more confident with the ball, and play more efficiently. All in all it's a deserved draw."