King, 29, has a chronic knee condition that prevents him from playing matches in quick succession. But he has learned to manage the injury and has played in eight of Spurs' 12 Barclays Premier League matches this season. It would have been more but for the hamstring problem that forced him off after an hour of the victory over Sunderland at the weekend.
"He felt his hamstring a little bit," said Redknapp. "Obviously with not training, it's a concern. That's what happens when you don't train - you do start to get a few twinges in games. It's a bit of a problem."
King's problem has halted his hopes of adding to his England caps - although elsewhere in Redknapp's squad, Tom Huddlestone and Jermaine Jenas earned recalls for the friendly against Brazil in Qatar on Saturday.
Aaron Lennon misses the match with an ankle problem but was close to returning for the Sunderland win so should be ready after the international break and will be looking to cement himself in Fabio Capello's World Cup plans.
Spurs midfielder Wilson Palacios has qualified with Honduras for the tournament in South Africa and is relishing his opportunity to shine.
"I am so happy that we have qualified for the World Cup," he said.
"The people of Honduras are still partying at home, and everyone is so excited about next summer."