Sandro lasted 74 minutes at Old Trafford before being substituted with cramp, but Redknapp says that his match-fitness will gradually return.
"I don't know long he'll need to be up to full speed," he told Sky Sports News. "But he hadn't played at all and there's nothing like matches, until you get on the pitch you can't bring it all together.
"It's taking on the nerves, the adrenaline, all the training in the world doesn't compensate for playing in 90-minute games, and that's what several of them lacked.
"Sandro will be fitter on Saturday than he was last week and he's going to be a great player for us."
The 25-year-old started just 49 Premier League encounters in his final three seasons at Spurs due to injury.