Coronavirus might have played a part in thwarting an attempt by Australian Jock Palfreeman to leave Bulgaria to attend the European Parliament.

Key points: The European Parliament has been closed to stem any further spread of coronavirus

The European Parliament has been closed to stem any further spread of coronavirus Mr Palfreeman was scheduled to speak on solitary confinement in Bulgaria

Mr Palfreeman was scheduled to speak on solitary confinement in Bulgaria It was not clear if he would have been allowed out of the country in the first place

Mr Palfreeman had been invited to go to Brussels on Thursday to speak at an event titled: Prisoners in Europe: A discussion on inhumane conditions in EU jails.

But the Parliament's President David Sassoli closed the institution on Tuesday to try to stem any further spread of coronavirus, leading to the cancellation of more than 100 events.

Mr Palfreeman, who has been in limbo in Bulgaria since his release from prison last September, told the ABC his planned visit had been "postponed because of coronavirus".

His morning session was described as a talk on "solitary confinement in Bulgaria".

It was not clear, however, that he would have been allowed out of the country in the first place.

His passport had been confiscated by the state, ever since former prosecutor-general Sotir Tsatsarov launched a highly irregular appeal to the Court of Cassation to have Mr Palfreeman returned to jail and his case reopened.

A composite image of CCTV stills from the night Jock Palfreeman stabbed a Bulgarian man in Sofia. ( Supplied )

Under Bulgarian law, the Court of Cassation has no jurisdiction over parole matters, and the Sydneysider is technically a free man.

There is currently no legal order which prevents him from leaving the country. But after the court agreed to hear the case, he was forced to give up the temporary passport he'd been issued.

In January, an obsolete travel ban, which dated back to 2011, was also formally overturned by the Sofia Administrative Court.

Several weeks ago, his passport was returned, but migration authorities have since appealed that decision of the administrative court.

Asked whether he would have been granted permission to cross the border, Mr Palfreeman said: "Legally, yes, but practically, no."

The case has appalled jurists and human rights defenders across Europe.

Space to play or pause, M to mute, left and right arrows to seek, up and down arrows for volume. Watch Duration: 5 minutes 38 seconds 5 m Jock Palfreeman fears what will happen to him if he returns to prison.

The Court of Cassation has yet to deliver its decision, five months after it heard the Government's appeal.

It had promised a decision within eight weeks.

In a post to his Facebook account, Mr Palfreeman said the Interior Ministry "continued to violate my rights by not allowing me to travel abroad, even to Brussels".

Mr Palfreeman served 11 years in a maximum-security jail over the stabbing death of a local student but was released on parole last September.

He was then detained in an immigration detention facility on the outskirts of Sofia until mid-October.