MELBOURNE: Serena Williams held a closed indoor training session at the Australian Open on Wednesday, increasing speculation about her fitness after she painfully rolled her ankle on court.

The world No.3 and hot tournament favorite twisted her right ankle during a 6-0, 6-0 demolition of Romania’s Edina Gallovits-Hall in her opening round clash on Tuesday.

The defiant 15-time Grand Slam champion claimed only a “fatal” injury would prevent her contesting the second round against Spain’s Garbine Mugu-ruza on Thursday.

But the reigning Wimbledon, Olympic and US Open champion moved her scheduled session from court 17 to the indoor training facility at Melbourne Park and it was closed to the media and public, tennis officials said.

Hundreds of spectators were ten-deep around court 17 until it became clear that the five-time Australian champion would not be making an appearance. Instead, she was hitting balls sindoors.

Williams did not appear to be in any discomfort when she was seen walking through Melbourne Park by an Agence France-Presse reporter with her coach, Patrick Mouratoglou.

Leading 4-0 against Gallovits-Hall, Williams fell heavily and lay on her back for an extended time, her face in her hands.

Despite this, she returned to defeat the world number 110 in 54 minutes, losing only six points in the second set.