Yoko Ono has been admitted to hospital with “flu-like symptoms”, her spokesperson says.
Elliot Mintz denied reports John Lennon’s widow had suffered a stroke.
He said Yoko Ono, 83, went to a New York hospital on the advice of her doctor and was expected to be discharged and return home later on Saturday.
Yoko Ono was married to John Lennon until he was murdered in 1980 outside New York’s Dakota Building, where she still lives.
An ambulance was called to the building at 21:00 on February 26, a Fire Department spokesman said.
Yoko Ono is spending the night in Mount Sinai Roosevelt Hospital in Manhattan.
She’s “OK, and she should be home tomorrow (Saturday)” said Elliot Mintz, after speaking to someone with her at the hospital.
Yoko Ono’s son, Sean Ono Lennon, also tweeted that his mother was doing well: “Hey guys it was only rumors from press: was NOT a stroke, just dehydration/tired. She is FINE. Thank you everyone for your concern.”
John Lennon’s killer, Mark David Chapman, faces his seventh parole hearing later this week.
Mark David Chapman, now 57, was jailed for 20 years to life after he confessed to shooting the Beatles singer outside his New York apartment in 1980.
He has come up for parole every two years since 2000 and has been turned down each time. In 2010, officials said his release remained “inappropriate”.
A decision on whether to release Mark David Chapman will likely be made public by the end of the week, a prison spokeswoman said.
John Lennon's killer, Mark David Chapman, faces his seventh parole hearing later this week
Mark David Chapman’s interviews with the parole board will take place at Wende Correctional Facility, a maximum-security prison in Alden, New York, where he is currently held.
He was transferred to the facility in May this year, where he was understood to have been placed in protective custody, though the reason was never made public.
In the past, John Lennon’s wife Yoko Ono is among those who have urged New York state officials to keep him behind bars, saying she fears for her own life and that of her two sons.
The former security guard, who has a history of mental illness, claims to have undergone a religious conversion while in prison.
On his last attempt at release – in September 2010 – Mark David Chapman is understood to have told the parole board he believed that “by killing John Lennon I would become somebody”.
“I wasn’t thinking clearly,” Mark David Chapman stated.
“I made a horrible decision to end another human being’s life, for reasons of selfishness.”
“I felt that by killing John Lennon I would become somebody and instead of that I became a murderer and murderers are not somebodies,” he said.
Denying parole at the time, the board cited his “disregard” for human life, adding: “This premeditated, senseless and selfish act of tragic consequence… leads to the conclusion that your discretionary release remains inappropriate at this time and incompatible with the welfare of the community.”