Local media say she is “conscious and stable” and she is due to undergo new tests in the next few hours to determine her state of health.
Dolores has already undergone treatment to remove a blood clot from an artery, in a procedure called a mechanical thrombectomy.
Her family are said to have asked the regional health service to respect her privacy while she remains in intensive care.
There has been no official comment from the hospital or any of her four children – but Ronaldo is expected to jet in from Italy and land around 4pm local time.
Ronaldo was spotted in Madrid this weekend to watch El Clasico clash with Barcelona.
Juventus’ Serie A clash with Inter Milan was postponed due to the coronavirus outbreak.
But having returned to Turin, he is now set to get in a plane once more and head to his home island of Madeira to be with his mum.
One local TV report described the next 12 hours as “decisive” and described Dolores’ stroke as “severe”.
It cited a close friend of Ronaldo as saying the Juventus star was considering travelling to Madeira today to be with her.
On Sunday, Dolores posted a selfie showing her enjoying a day out on her home island.
She looked happy and relaxed as she posed for the photo by a monument in Machico, a small city on Madeira’s east coast which was the island’s first settlement.
The social media fan, who has more than two million followers on Instagram, wrote alongside the photo: “Happy Sunday to everyone.”
Her daughter Katia responded with a heart emoticon and the words: “My darling mum.”
The previous day she posted another photo thought to have been taken from the roof terrace of her home on the island with a message saying: “Good weekend to everyone.
“Take advantage of this sun to enjoy a stroll, but don’t forget to protect your eyes with sunglasses.”
There was no immediate response to the news of Dolores’ stroke from Cristiano’s representatives in Portugal.
At the start of last year Dolores revealed she was “fighting for her life” after a new cancer drama.
She beat breast cancer after being diagnosed with the disease in 2007.
Ronaldo then donated £100,000 to the hospital that saved her mum’s life two years later.
In February last year, ahead of a trip to Italy to celebrate her footballer son’s 35th birthday, she admitted to new health problems.
She told a Portuguese TV station in a interview: “I was operated on another breast in Madrid, I’ve had radiotherapy and now I’m fighting for my life.”
And in November, Dolores launched a sensational rant in defence of her son, saying he’s been held back by the “football mafia”.
She claimed: “There is a mafia. That’s the right word to define it. Yes, there is a mafia in football.
“If there wasn’t a football mafia, my son would have more [individual] international trophies.
“If you see everything that happened, you will realise that it is the mafia.
“If he was Spanish or English they would not do what they did to him. But since he’s Portuguese and from Madeira…well, this happens.”
And Dolores was an ardent supporter of her son over the rape claims Ronaldo faced.
In October 2018, news emerged of a new police investigation against him over Kathryn Mayorga’s claims the footballer raped her at a hotel in Las Vegas.
Dolores and her daughter Katia posted pictures of the footballer in a Superman cape with matching messages which read: “I want to see who has the courage to put this photo on their profile for a week and make a chain for him…
“For Portugal, for him, for us and for the union of our people, for justice. He deserves it.”
The cartoon-style picture of Ronaldo carried two hashtags in Portuguese. One translated as #Ronaldo, we are with you to the end and the other #Justicacr7 as #Justice for CR7.”
She also welcomed news last July Cristiano would not face criminal charges when prosecutors said Mayorga’s allegations “cannot be proved beyond a reasonable doubt”.
Dolores took to social media to insist she always knew Cristiano had never done anything wrong.
The proud mum whose alcoholic ex Dinis drank himself to death in 2005 when their son Ronaldo was just 20, posted a picture of her by a pool in a matching leopard-print top and trousers.
She said: “Face of serenity of someone who knows her children.”
She finished her comment with the hashtags “justica” and “familia” – Portuguese for “justice” and “family”.