Sandro was substituted after only 11 minutes after appearing to suffer concussion and club doctors decided to bring the Brazilian midfielder off the field.
Redknapp said the player would have been fit to continue playing later in the half.
Harry Redknapp: "You couldn't wait 10 or 15 minutes with 10 men, you just couldn't do it.
"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."