Justine Henin-Hardenne admitted that she had known a retirement was likely before stepping on the court in Saturday's Australian Open final.
Henin-Hardenne was looking for her fifth Grand Slam title
The Belgian was forced to withdraw when trailing Amelie Mauresmo 6-1 2-0.
"It's been a few days I wasn't feeling well," she said. "My stomach was very upset and last night I didn't sleep a lot because it got worse and worse.
"Two weeks now I had to take anti-inflammatories for my shoulder, and that killed me a little bit."
She added: "I had to double the dose of my anti-inflammatories the last few days because my shoulder was painful, and it's probably I just had a very bad reaction to that."
The problem is unrelated to the viral infection which sidelined Henin-Hardenne in 2004, but it was still too much for her to cope with on Saturday.
"I had no legs today. I couldn't move. When the stomach is so upset and so inflamed you just don't have any energy," she said.
"I knew at the beginning of the match I couldn't win it. I just really tried to stay in the match, but there was no chance for me."
Henin-Hardenne described the disappointment as "one of the biggest" of her career but paid tribute to Mauresmo.
"I think that she did her job perfectly. She kept the ball in the court.
"She felt probably I wasn't feeling good and couldn't move very quickly. So she did a good job when we see the circumstances.
"It's great when you win a Grand Slam after a big fight, for sure, after a normal match. But I'm sure she enjoys this moment, and she deserves that."