The left-back signed for the Old Trafford giants in a £4million deal from Vitesse Arnhem last summer.
But the 24-year-old, who was brought up on a travellers' camp in Holland, struggled to settle into life in Cheshire.
Buttner told The Sun: "I now know about homesickness. I'd think about my family and friends at home many times.
"How they were, what they were doing, little things like that.
"But I did not give up and I have my girlfriend Laura and brother Denny to thank for that.
"They were always there for me in England. I could call on them any time. I needed their warmth.
"I'm a fighter. But had I been on my own, I'd have got on a plane back to Holland a long time ago."