It was the miracle that set Pope John Paul II on the road to sainthood and provided faithful followers with proof of his holy powers. But hopes that the former pope's canonisation would be fast-tracked by Sister Marie Simon-Pierre's recovery from Parkinson's disease have been set back by reports that the French nun has fallen ill again.

Simon-Pierre described three years ago how she regained her health after a night of prayer to the then recently deceased Polish pontiff. John Paul also suffered from Parkinson's disease, which is incurable.

"It's like a second birth," she said at the time. "I feel like I've discovered a new body, new limbs."

In 2007 Simon-Pierre could barely move her left side, could not write legibly, drive or move around easily and was in constant pain.

Her disease worsened after the pope's death, and her order prayed for his intervention to ease her suffering. Then after writing his name on a paper one night, she woke up the next day apparently cured and returned to work as a maternity nurse with no traces of the disease.

But according to the Polish daily newspaper Rzeczpospolita, one of the doctors charged with scrutinising the nun's case believed she might have been suffering from a similar nervous disease, not Parkinson's, which could go into sudden remission. A report on the paper's website went further, saying that the 49-year-old nun had become sick again with the same illness.

The Vatican was making no comment on the grounds that the late pope's case was still under examination.

Although no date has been fixed for the late pope's beatification, there had been an expectation that it would be announced in mid-October. His case was fast-tracked by his successor, Pope Benedict, and the anniversary of John Paul's election falls on 16 October.

The first sign that all might not be as it should be came when the Vatican fixed the canonisation of six new saints for the following day, a Sunday, making a beatification the same weekend impossible.

Vatican sources stressed that the panel of doctors which will examine the evidence relating to Simon-Pierre's recovery was not due to meet until April, when it will consider a report by two medical experts.

Beatification is an intermediate step on the road to canonisation, though not all of those declared "blessed" go on to become saints. Beatification requires at least one miracle. A second is needed for sainthood.

The Vatican, whose congregation [department] for the cause of saints deals with canonisations and beatifications, has been under relentless pressure to speed up John Paul's progress. On the day of his funeral in 2005 there were unparalleled scenes in St Peter's Square, when the crowd took up a chant of "santo subito", or "saint straightaway".