Traditionalists have openly challenged the Argentine pontiff, who is considered by some Catholics to be undermining key doctrinal teachings with his liberal leanings and push for a more compassionate church.
Francis has reached out to gay believers, famously saying "Who am I to judge?" and has allowed divorced and remarried believers to receive communion in some cases.
His illness has "given more oxygen" to those seeking to protray him as weak or those who hope he will follow his predecessor Benedict XVI and resign, Robert Mickens, editor of the French Catholic newspaper La Croix International, told AFP.
The 86-year-old pontiff, who has a series of health issues, has previously said he would quit if he no longer felt able to do his job -- although he insisted in February it was not on his agenda.
The three nights he spent in Rome's Gemelli hospital for bronchitis, however, have sparked "feverish agitation" among both his allies and critics, said Massimo Franco, Vatican expert for Italy's Corriere della Sera.
"Speculation on the near future of his pontificate becomes less theoretical," Franco wrote Friday.
In 2013, Benedict XVI became the first pope since the Middle Ages to resign, citing his declining physical and mental health.
Conservative Benedict is credited as having served in retirement as a moderate influence. After his death on December 31, opposition to Francis from top convervatives intensified.
Francis has cautioned against papal resignations becoming the norm.
He has however left open the possibility of following in Benedict's steps, even painting a picture of what his retirement might look like, saying he would live in Rome, possibly as a priest, and no longer wear white.
Vatican expert Iacopo Scaramuzzi said Francis's enemies were fuelling speculation through an old tactic of using his health "as a battleground -- inflating partially true news or making it up entirely".
In October 2015, when the pope was pushing the Church to be more forgiving to remarried divorcees, enraging traditionalists, the Vatican had to deny rumours Francis had a brain tumour.
"The game is being played again now," Scaramuzzi said, amid talk that doctors found a tumour when Francis underwent a colon operation in 2021 and he now has widespread cancer.
The pope denied those reports himself in an interview last year.
Francis is well aware that the febrile wrangling over his successor goes into overdrive when he is sick.
After the 10-day stay in hospital in July 2021, he joked that "some people wanted me dead" and cardinals were already set to replace him.
Leaving the hospital Saturday, he quipped "I'm still alive".
The pope, who admitted last summer that he had to slow down, uses a wheelchair and walking stick for knee pain, and said in January that the problems with his intestine have returned.
But the world knows little more.
While Francis gives occasional titbits on his health in interviews, the Vatican provides barely any information, creating fertile ground for conspiracy theories.
This week, the Vatican initially said he was going into hospital for pre-planned tests, before revealing he was suffering breathing difficulties and was diagnosed with bronchitis.
"Whether there's more to his overall health, if he's got a tumour as some have suggested, we don't know, we just don't know," Mickens said.
He said Francis deliberately keeps information to himself, "because he knows that this old Vatican machinery tends to run itself, and run the pope, and he doesn't want that".
But the lack of transparency also means conjecture as to how long Francis has left.
"It becomes a real sport, the Death watch", Mickens said.