Redknapp said he had an audacious bid for England centre-back Ferdinand rejected at the start of the season, with United telling him he was not for sale.
"I can't ever see us getting Rio now. I was interested. Last year, I tried. I tried at the start of the season," Redknapp said, according to the Guardian. "When he was on the teamsheet against Chelsea in the Champions League, I thought Man United had got a much, much better chance of getting a result and it proved that way."
Redknapp wants to make Tottenham Champions League regulars and in looking at the Premier League clubs ahead of his - the likes of United and Chelsea - he has identified that the blueprint for success includes a core of strong-willed generals amongst a cast of talented imports, the latter of which Tottenham already have an increasing number.
Redknapp urged chairman Daniel Levy to ensure big personalities, along with big talents, are among those on the club's summer shopping list.
"I've said many times to the chairman, it's not always about the best players, it's about getting characters in your football club," Redknapp said. "Chelsea have had it over the years, whether it's John Terry or Frank [Lampard], and Man United have had it with [Ryan] Giggs, Ferdinand and [Nemanja] Vidic.
"William [Gallas] has come in and given us experience and we've got Michael [Dawson] at the back but in the long term I still feel that you need to find another one or two if you're going to keep progressing, that type of real character, who has opinions and that will to win around the dressing room - a few leaders. You can't have too many at your club. That's why I tried to take Phil Neville from Everton in January."