The New Zealand international has been a mainstay of QPR’s side this season, under both Redknapp’s predecessor Mark Hughes and the current manager.
However, Toronto’s managerial offer succeeded in luring the former Blackburn Rovers centre-half, who only joined the Hoops as back-up and never expected to feature on a regular basis, to the MLS.
Remarkably, Nelsen made 21 Premier League appearances for the Hoops, forging an impressive partnership with Clint Hill in recent weeks, after joining in the summer on a free transfer.
And QPR manager Redknapp says Nelsen will be missed.
“The big one was losing Ryan Nelsen. Because he had been so good for us, that was the key,” said Redknapp.
“We lost a real leader he had been absolutely fantastic for us.”
QPR have moved swiftly to replace Nelsen, with the Kiwi’s former Blackburn team-mate Chris Samba arriving at Loftus Road after completing a £12.5m switch from Anzhi Makhachkala.
On Friday, Redknapp revealed that he had drawn up a fanciful wish list of centre-halves which he would like to sign – names included Rio Ferdinand, John Terry, Nemanja Vidic and Samba.
But the QPR boss didn’t anticipate club owner Tony Fernandes pulling off a massive coup and signing one of his fantasy targets.
“I didn’t know anything about Chris Samba move, it was completely out of the blue,” he added.
“He sat down with me ten days ago and said who would you take, if you could anyone. I named Vidic, Ferdinand, Terry and Samba. I have tried to Samba loads of times in the past.
“The chairman just said to me that he was close to getting me one of those players on the list but he wouldn’t tell me who it was.
“And that was how it went. We sat there in the office me, Kevin (Bond) and Joe (Jordan) all guessing who it would be.
“He told me the day before he got him.”
However, Redknapp believes Samba’s arrival doesn’t necessarily guarantee QPR’s top-flight survival, with the Hoops boss adamant the Congo star is merely replacing a top-class outgoing defender.
“It doesn’t mean we are going to stay up just because we have bought Samba.
“It is a top centre-half replacing a top-centre half. If Ryan Nelsen had stayed here then I wouldn’t have had to buy Samba.
“Other clubs spend money down there; Villa have spent big money down there.
“People think they have bought just kids, go back to Darren Bent, you can go through a list of players there and they have spent good money as well. Richard Dunne and other players have all cost good money.”
MORE: The latest football news