A top aide to France's first lady says she will remain in hospital for several more days to recover from the shock of a tabloid report that her partner, François Hollande, is having an affair with an actor.

Valerie Trierweiler's chief of staff, Patrice Biancone, said on Monday she could stay in hospital for a further six or eight days. She was initially expected to leave the hospital on Monday. He said she suffered a "very strong emotional shock" and needed rest. One official said she was receiving treatment for "a severe case of the blues".

Hollande has never married. He and Trierweiler have lived together since 2007 and she occupies the so-called "madame wing" of the presidential palace.

Meanwhile, the "Hollande affair" has taken an unexpectedly sinister turn with claims – and counter-claims – that the flat used for the president's alleged love tryst with an actor was linked to the Corsican mafia.

French media reported that the apartment where François Hollande met Julie Gayet was lent to her by a friend who was involved with two mobsters.

However, the friend, Emmanuelle Hauck, denied her ex-husband Michel Ferracci, who was given an 18-month suspended sentence in connection with money-laundering last November, had ever owned, rented or lived in the property and threatened to sue for defamation.

It was later revealed that after splitting from Ferracci, Hauck lived with François Masini, who was shot dead last May in an apparent gangland killing.

Meanwhile, Hollande was preparing for a key press conference on Tuesday in which he is expected to announce new goals and a timetable for reforms in front of 600 French and foreign journalists.

Jean-François Copé, president of the Union for a Popular Movement party, described the scandal as "disastrous for the image of the presidential role" while declaring his commitment to France's privacy laws.

French newspaper Le Parisien reported that Trierweiler, 48, is ready to forgive Hollande, and claimed the president told his partner Closer was making public his alleged affair just a few hours before the magazine hit the newsstands.

Frédéric Gerschel, a journalist at Le Parisien who was reportedly in contact with Trierweiler, claimed Hollande did not spare her the details.

"He denied nothing, not the escapades on scooter with his bodyguard in the middle of the night, nor the frequency of the secret meetings, or the date when this 'love affair' as the foreign press has baptised it, started several months previously," he wrote.

One of Trierweiler's friends told the paper: "The news hit Valérie like a TGV hitting the buffers. She was completely stunned. Of course she had heard the rumours going around Paris for weeks, but she wanted to believe they were false. To her, they [Trierweiler and Hollande] are still a couple".

Trierweiler was taken to hospital on Friday after Closer magazine published seven pages of pictures of Hollande visiting the apartment in Paris's chic 8th arrondissement and apparently staying overnight.

The magazine showed photographs of a man in a black helmet, alleged to be Hollande, being accompanied to and from the apartment by a bodyguard on a scooter on 30 and 31 December.

Hollande, 59, who is accompanied on official engagements by Trierweiler, reacted to the magazine's claims in a personal capacity with a threat to sue Closer on the grounds that it had invaded his privacy.

The article was removed from Closer's website following what the magazine described as a "very clear" legal injunction from Gayet's lawyers. Hollande has not denied the affair.

Ministers and Elysée officials said the affair was none of the public's business, a sentiment echoed by a poll, published in the Journal du Dimanche, which found 77% of French respondents believed the affair was a personal matter, while 84% said their opinion of Hollande was unchanged by the revelations.

However, Trierweiler appears to elicit little sympathy. A poll on the website of the magazine Le Point showed a majority of readers want her to go. Asked on Saturday whether Hollande should announce their separation, 89.2% of the 13,136 people who voted said yes and 10.8% said no.

Ségolème Royal – Hollande's partner of 23 years and mother of his four children, whom he left for Trierweiler – was drawn into the scandal on Sunday during an appearance on France 2's news programme.

"I don't want to feed the saga with a little sentence which is very, very far from French people's concerns," she said. When the presenter asked whether the issue was "not political", Royal said: "We should turn the page and get back to work."

It was not clear whether she was referring to Hollande, to herself and the president, to Trierweiler, or to the French public as a whole.

The Gayet scandal has come at an unfortunate time for Hollande, who hopes to rebuild confidence in the government's handling of the economy.

In a new year message, the socialist leader made overtures to French bosses – raising eyebrows among the leftist elements of his party – and is expected to flesh out details of a "responsibility pact" with employers who have complained that high taxation is hampering their hiring ability.

According to a poll published in Le Parisien on 4 January, only 31% of French people find Hollande "competent", although 56% say he is "likeable".