With only 60 days left before the Games, the 32-year-old athlete broke her right thighbone after taking a nasty spill on the slippery Ultra track oval last Wednesday.
Manahan, a bronze medalist in the same event of the 2003 Vietnam SEA Games, was doing a 200-m speed work under a drizzle when she lost her footing.
She was immediately brought to the Cardinal Santos Memorial Hospital in San Juan where she underwent operation. A metal plate was used to correct the damage.
Manahan has been declared out of danger and out of the SEA Games where the Filipino tracksters are eyeing the overall crown with a projected 15 gold medals.
Manahan is the RP record-holder in womens 20 km walk with a time of 2 hours 22 minutes 03.1 seconds, which she set during the 2001 National Open.
Unconfirmed reports said she was a gold medalist in the arnis competition of the 1991 Manila SEA Games.
Athletics chief Go Teng Kok said its a pity to see an athlete get hurt in her bid to give honor to the country.
"Shes been working very hard for this SEA Games and its a pity she had that accident. Her dedication mirrors how hard our athletes train," said Go.
Track coach Jojo Posadas said the accident may have been caused by the patches of mud being left on the oval by those playing football especially on rainy days.
"Minsan kasi ang mga football players na tumatawid sa track galing sa field nila nag-iiwan ng putik. Nagiging madulas ito kahit matuyo na," said Posadas.