The manager said the winger 'hadn't been feeling great all day' and had to be replaced by Jermaine Jenas as they ended up losing the Champions League quarter-final, first leg 4-0 against Real Madrid.
"We lost Aaron just as the teams were walking on the pitch," Redknapp told the Spurs website. "He didn't feel well enough to play so we had to change straight away.
"He hadn't been feeling great all day. I said 'are you ok?' and he said 'I don't feel like I have any strength or energy to run', so I had to pull him out.
"He went out to warm-up, came in and just said he didn't feel well and wasn't fit enough to play. There is nothing you can do."