Polish freedom icon Lech Walesa was hospitalised for tests on Saturday, forcing him to give up plans to join an anti-government street protest next week.
The 73-year-old Nobel peace laureate, who is being treated in the northern city of Gdansk for high blood pressure, had been due to join Monday's demonstration in Warsaw, declaring the rightwing government "impudent and harmful".
"For several weeks I've had swollen feet, but I didn't think it was anything serious," the former president told regional news site Trojmiasto.wyborcza.pl.
"At noon I found myself at hospital. I have very high blood pressure and the doctors decided to put me to bed for observation," he said.
The Polish government is being probed by the European Union over perceived threats to the rule of law, and Walesa has previously questioned whether Jaroslaw Kaczynski, the powerful boss of the governing Law and Justice (PiS) party, is seeking to turn Poland into "a dictatorship".
On Saturday, acknowledging he would not be able to take to the streets Monday as planned, he called on protesters to "make sure it's a peaceful demonstration, that the situation does not get out of control or turn into a civil war".
As for himself, he said, "All is not lost. We will meet in a month, on August 10. I hope the doctors will have put me back on my feet by then."
Monday's protest has been organised in opposition to a monthly march carried out by Kaczynski in memory of his twin brother Lech, Poland's president at the time, and 95 other people who were killed when the presidential jet crashed in Russia in 2010.
Opponents say Jaroslaw Kaczynski uses the monthly event to mobilise supporters and attack centrist critics.
Shipyard electrician Walesa won the Nobel Peace Prize in 1983 for leading Solidarity, the Soviet bloc's only free trade union, and became Poland's first democratically elected president in 1990.
His boldness in standing up to the communist regime is still widely respected, but his divisive presidency earned him scorn from many Poles.
© 2017 AFP