Sandro was withdrawn from the pitch just 11 minutes into QPR's clash against Southampton on Saturday after receiving a heavy blow to his head.
The QPR midfielder appeared to have suffered concussion, leading to his substitution under the direction of club medics.
Club medics have the final say on whether players are substituted after suffering head injuries, according to Premier League rules.
Redknapp understands medics must take no risks with a player's health but the implementation of a temporary substitution would allow sufficient time to assess head injuries.
"You couldn't wait 10 or 15 minutes with 10 men, you just couldn't do it," he said.
"So you couldn't give medics that amount of time to look at a player.
"But it doesn't sound the worst idea for a temporary replacement, so that the doctors could have a longer look at the player with the potential head injury.
"Medical people have got to be so careful, they can't take a chance because if anything went wrong there would be massive trouble.
"If someone is very bad, you cannot expect them to carry on because if something went wrong we would all be very sorry.
"At half-time, there didn't seem to be a lot wrong with Sandro. He was fine in the changing rooms, he didn't look too bad at all but obviously the doctors have got to err on the side of caution."
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