The 34-year-old annouced his withdrawal from international selection on Wednesday with 81 caps to his name, after revealing on Monday that he hopes to earn a new contract with United.
Ferdinand was recently voted in the Professional Footballers' Association Team of the Year, and he admitted his decision was heavily influenced with the view to extending his domestic career.
"I think I owed it to Manchester United to do that but it wasn't easy, I'm not going to lie," he told MUTV.
Ferdinand is yet to feature under current England boss Roy Hodgson following his exclusion from the Euro 2012 squad for "footballing reasons", before rejecting a call-up in March to face San Marino and Montenegro in a World Cup 2014 qualification double-header.
And the defender - who captained the Three Lions on seven occasions - says reduced commitments will allow him to "give my everything" to United.
"I'm as passionate as the next man and I've always loved doing that. But there comes a time when your body tells you what to do.
"If I want to remain fit and well and playing consistent football at the top level it had to give somewhere and international football was that. I had a good stint in international football but now I want to give my everything to Manchester United."