Davies returns to USA on loan
The 24-year-old Davies was playing with French first division club Sochaux before suffering serious injuries in the accident on October 13, 2009.
"We are really pleased to have concluded a deal that will bring Charlie to United," said general manager Dave Kasper.
"Charlie spent 10 days with us in our first pre-season camp and underwent a full battery of physical and medical testing. He simply looks terrific.
"Coming in, we weren't sure where he would be but he's great physically, has impressed with his mental approach and we're excited to see him on the field with us this season."
Davies has never played in MLS having moved from youth club Westchester Flames to Swedish team Hammarby in 2007.
Prior to the accident, Davies had become a regular in the U.S. national team and impressed with his performances in their run to the Confederations Cup final in 2009.