The 35-year-old was unveiling as QPR's latest signing on Monday but insists he could have extended his Old Trafford contract if the Welshman was appointed as permanent manager.
The veteran center back brought an end to his trophy-laden 12-year stay at Old Trafford when his contract expired last season and subsequently reunited with Harry Redknapp, who he worked under at West Ham.
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"[Giggs and I] had that chat when he got the job, he had to look at it as if he would still be there and he did tell me I would have stayed and been a part of his plans," Ferdinand said at his QPR unveiling. "But things change quickly, the new manager came in and wanted a new direction. I dusted myself down and moved on.
"I said at the time that Man United would have to tell me they didn't want me for me to leave the club. That's what happened - they said 'thank you and goodbye.'
"It has to be that way. The club is bigger than any player. I'm here now and I'm glad that Harry and [QPR chairman] Tony Fernandes gave me the chance to come here."
Ferdinand also confirmed he had other offers but the lure of moving back to London helped make the decision.
"I play to win whether that's a match or in training. We have to put points on the board. That's what we did at Man United that's what we'll do here. A successful season is staying in the Premier League," he said. "There were teams in the Premier League and teams abroad, but when Harry gave me the call and the chance to return to London [I could not turn it down]."