The midfielder moved to White Hart Lane for £5.5m over the summer but, despite his Football Writers' Footballer of the Year status, the Spurs boss says that the board weren't convinced.
"The hardest signing for me was Scott Parker," said Redknapp.
"It wasn't a deal that the club were crazy about, and I could see their point of view. Scott had a four-year contract at West Ham and he was on big money, by our standards. Tottenham don't pay the wages that Chelsea or Manchester City do, so there would be quite a gap.
"There was a feeling that bringing in Scott, 31 years of age and with no sell-on value, could be a problem. I argued that it was what he could give us this year and next that could make the difference. Daniel [Levy, Tottenham chairman] backed me on that."
Spurs travel to one of Parker's former clubs, Newcastle United, in the Premier League on Sunday.