Pat Lampard, the mother of Chelsea midfielder Frank Lampard, died Thursday at the age of 58.
She had been admitted to hospital with pneumonia ten days ago, the dpa reported.
Lampard missed Chelsea's Premier League games against Wigan Athletic and Everton last week to be with her, but played in Tuesday's 1-1 Champions league semi-final draw against Liverpool after she showed signs of improvement.
A Chelsea statement said: "It is with great sadness that we have to inform you that Pat Lampard passed away this afternoon.
"Frank would like to acknowledge and say thank you for the compassion shown to him by the manager Avram Grant and all the staff at Chelsea Football Club during what has been a terribly traumatic period for him and his family.
"Frank and his family would also like to thank all the people who have been inundating them with wishes of support."
The news leaves Lampard a major doubt for Saturday's crucial Premier League fixture against Manchester United.
Liverpool, who face Chelsea in the second leg of their semi-final next Wednesday, have expressed their condolences.
"It is difficult for him, especially before these important games," said manager Rafa Benitez.
"He has our sympathy because for him this is very, very bad news. Some of our players are mates with him from the national team, so everyone feels the same."