Justine Henin-Hardenne was put on a drip on Friday night after suffering dehydration less than 24 hours before her U.S. Open final date with fellow Belgian Kim Clijsters.
The second seed was treated by medical staff after cramping during her late-night 4-6, 7-5, 7-6 semi-final win over American Jennifer Capriati.
She and Clijsters are scheduled to walk out for the final on Arthur Ashe stadium at 8 p.m. (0000 GMT) on Saturday.
But a statement from the WTA Tour which represents women's tennis said that Henin's fitness would be re-evaluated on Saturday afternoon.
Henin-Hardenne beat Clijsters in the French Open final in June, but Clijsters enjoyed a relatively relaxing time on Friday, reaching the final with a 6-2, 6-3 win over Lindsay Davenport.
Henin-Hardenne said she should have called a trainer during her three-hour, three-minute match with Capriati but said fears of attracting criticism stopped her.
"I will only go on court (in the final) if I am able to compete," Henin, lying down and with a drip inserted into her arm, said from the U.S. Open medical room.
"Out there tonight, I was cramping in my left leg when I tried to serve.
"But a lot of people have talked badly about me in the last few weeks, so I made a big mistake in (not calling for the trainer).
"I needed to see a trainer...I will not make a mistake like that again."
Henin-Hardenne has attracted criticism especially in the U.S. after her French Open semi-final victory over Serena Williams when the pair disagreed over whether a point should be replayed.
Earlier this month Clijsters also suggested an injury timeout her compatriot took during the final of Acura Classic in California amounted to gamesmanship.
Henin-Hardenne was delighted with her win, averting danger time and again when Capriati moved to within two points of victory.
"I felt the match was almost over sometimes," she said.
"But I was so proud of the way I did what I did. I think she got nervous as well."
Henin beat Clijsters in the French Open final in June, but while Henin was struggling with her fitness in the early hours of Saturday morning, Clijsters was sleeping.
She had earlier secured a smooth path to the final, beating Lindsay Davenport 6-2, 6-3 in their semi-final.
