The Stamford Bridge club have offered Lampard, 29, their full support as he comes to terms with the loss.

England international Lampard missed the recent Premier League games against Wigan and Everton after his 58-year-old mother Pat was admitted to hospital with pneumonia.

He then resumed training earlier this week ahead of Tuesday night's Champions League semi-final first leg at Liverpool after his mother had showed signs of improvement - only for her condition to deteriorate rapidly.

A statement from Lampard's agent, Steve Kutner, read: "It is with great sadness that we have to inform you that Pat Lampard passed way 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."

Lampard is now expected to receive further compassionate leave to be with his family.

Pat Lampard was wife to Frank senior, the former West Ham and England defender, while her sister married Harry Redknapp, the Portsmouth manager, who is the father of ex-Liverpool and England midfielder Jamie Redknapp.

It is also uncertain whether Lampard will feature in Wednesday night's Champions League semi-final second leg, with the tie delicately poised at 1-1.

A statement from Chelsea read: "Everybody at Chelsea Football Club is absolutely devastated to hear the tragic news of the passing away of Pat Lampard, Frank's mother.

"Our sincerest and deepest condolences go out to Frank, his father Frank senior, sisters Natalie and Claire, and to their immediate family and friends.

"Pat was a very familiar face to many people at Chelsea.

"Her unswerving support for her son's career was evident at virtually every game that Frank participated in. Regardless of where it was being played, she would always be there to watch him with Frank's dad. Pat will be deeply missed by everyone at Chelsea."

The statement concluded: "The club will be offering all the support it can to Frank and his family at this time."

Liverpool have passed their condolences on to Lampard and his family.

Manager Rafael Benitez said: "It is difficult for him, especially before these important games.

"He has our sympathy because for him this is very, very bad news."

Benitez added: "Some of our players are mates with him from the (England) national team, so everyone feels the same."

On the pitch, meanwhile, Chelsea need to beat United if they are to join them at the top of the table, with the gap currently three points with three games left to play.

In Lampard's absence, Germany captain Michael Ballack looks set to have an important role to play in midfield.

The 31-year-old feels he is in good shape for the final push, after having been forced to sit out the early part of the campaign because of an ankle problem.

"It's always important to be in good shape and at your best at the end of the season, when it's all about the championships," Ballack told German newsmagazine Der Spiegel.

"I didn't play for half a year, because of my ankle injury, which is why this season doesn't feel drawn-out to me.

"I feel fit and I'm highly motivated."

Ballack joined Chelsea on a reported £130,000-a-week deal following a free transfer from Bayern Munich after the 2006 World Cup.

The veteran German maintains he has no intentions of moving on again.

"That isn't part of the plan, but it wouldn't bother me either, because I have the most important transfers behind me," he said.

"The decisions a footballer makes at 18 or 23 are the important ones, the ones that count.

"I can't make any especially big mistakes anymore."

Ballack feels comfortable at Chelsea.

"It's exactly what I wanted," he said. "You only develop if you have good players next to you and when every game is a challenge.

"When I was with Bayern Munich, I won the double three times in four years, and then we were often eliminated early on in the Champions League.

"I wasn't excited anymore about winning the German championship yet again. I was looking for a new challenge."

Ballack added: "There are more exceptional players than in Munich, and it's a constant fight for positions and roles."