The 29-year-old has given an insight into her relationship with the world number one golfer, who began dating the skier following his divorce from wife Elin Nordegren.
The 37-year-old's marriage crumbled when reports emerged claiming that the sportsman had a string of affairs.
"He's very mentally tough," Vonn told the Today Show. "He's a grinder.
"He works extremely hard, and he's obviously also had an ACL injury as well and had the same surgery, so he knew what I was going through.
"He said just be patient, keep working hard, and everything is going to turn around. It really helped me get through it."
The couple have been in a relationship for seven months.