WARSAW — Speculation about a potential changing of the guard in Poland's ruling party is taking hold in government circles, after officials confirmed the country's de-facto leader Jarosław Kaczyński was admitted to hospital due to a "life-threatening situation," not a knee injury.

Kaczyński, the powerful head of Poland's ruling Law and Justice party, has been missing from the public eye since late April and was initially said to be suffering from a "osteoarthritis" in his right knee.

"Jarosław Kaczyński's state of health was such that not accepting him to the hospital would have threatened his life, and therefore he was admitted in an acute manner," Poland's health minister, Łukasz Szumowski, told Polish radio.

The Law and Justice party's spokesperson, Beata Mazurek confirmed the statement, but declined to provide details.

Kaczyński, who will turn 69 on Monday, was released from hospital on June 8, after being treated for more than a month. He didn't show up Saturday for a ceremony — attended by Prime Minister Mateusz Morawiecki and senior PiS leaders — to unveil a monument in the port city of Szczecin for his twin brother Lech, who died in a plane crash in 2010 while serving as Poland's president.

Information about the state of Kaczyński's health has been a tightly kept secret, but his absence has nevertheless prompted speculation about a potential successor.

Interior Minister Joachim Brudziński sharply pushed back against it, saying that, "All those dreaming about replacing Kaczyński, must get armed with a very long patience." The party's first deputy chairman and a close Kaczyński ally said in a TV interview: "The chairman is in full control of what is going on in the party and is not planning a political retirement."

But Brudziński's rebuke only fueled the chatter in Warsaw about what or who might come next. He's a member of the so-called convent of loyal Kaczyński supporters, and himself considered to be a potential contender to the PiS leadership post.

Before becoming interior minister in a January government reshuffle, Brudziński was PiS's all powerful executive secretary, a role that put him in charge of party structures and granted him a firm grip on the organization.

Brudziński is not the only senior figure who is well-placed to take over. A recent poll, conducted by pollster IBRIS for the daily Rzeczpospolita, showed 14.4 percent thought Morawiecki would be best placed to replace the PiS leader, over 9 percent for Brudziński and 8.6 percent for former Prime Minister Beata Szydło (42.8 percent said they didn't know).

Morawiecki, who turns 50 on Wednesday, emerged last year as an unexpected Kaczyński protégé. The slick former banker replaced a reclusive Szydło as prime minister in December and started a charm offensive in Brussels, at Davos and in other Western capitals to improve Poland's image, which has been tarnished by judiciary reforms the European Commission considers to be a breach of the rule of law.

The prime minister may also be an attractive candidate in PiS circles because he presents himself as a far-right politician: At a February conference in Munich he referred to "Jewish perpetrators of the Holocaust," and in his first interview Morawiecki said it was his "dream to re-Christianize Europe."

Another possible contender to replace Kaczyński is justice minister Zbigniew Ziobro, the brain behind Poland's judiciary reform. Ziobro, 47, is the leader of the small Solidarna Polska party that joined the PiS electoral ticket.