Diane Abbott has a long-term condition which may have played a part in her below-par interview performances during the general election campaign, a shadow cabinet colleague has said.
Ms Abbott pulled out of two major election events yesterday due to illness and Labour leader Jeremy Corbyn announced this morning that shadow home affairs spokeswoman Lyn Brown is to stand in for her during her period of ill-health.
West Ham MP Ms Brown was among a number of shadow ministers who quit the front bench last year, saying that Labour needed a new leader "for the good of the party and the country".
However, she returned to Mrs Abbott's home affairs team three months later as shadow minister for policing.
Ms Abbott, a close Corbyn ally, has come under relentless fire from Conservatives following an interview with LBC radio in which she forgot figures for Labour's police funding plans and an appearance on Sky News when she struggled to discuss details of a security report.
She was replaced by shadow foreign secretary Emily Thornberry for a debate on BBC Radio 4's Woman's Hour and a hustings organised by the London Evening Standard.
She tweeted today that she "will rejoin the fray soon", but gave no further details.
Touched by all the messages of support. Still standing! Will rejoin the fray soon. Vote Labour!— Diane Abbott (@HackneyAbbott) June 7, 2017
Labour's international trade spokesman Barry Gardiner said he had been told by party officials that the shadow home secretary was suffering from a long-term illness.
"Diane is clearly not well and I understand that it is a condition which has been diagnosed and is long-term," Mr Gardiner told TalkRadio presenter Julia Hartley-Brewer.
"I think anybody who has seen her in the past couple of weeks would realise that she was showing that she was not well, in the way in which she had been operating ...
"Everybody is aware that Diane didn't perform well in a couple of programmes, but what we didn't know was why and I think that has now become clear."
He added: "I am sorry for her, obviously, that she has got this condition and clearly it is now a matter for her to get properly diagnosed and properly treated and I wish her well in her recovery."
Mr Gardiner later declined to confirm his comments to the Press Association, saying that it was a matter for Ms Abbott to decide what details of her health should be made public.
It is understood that her condition is not one which would prevent her eventual return to work once she has recovered.
Shortly before announcing Ms Brown's temporary appointment, Mr Corbyn told BBC Breakfast that Ms Abbott had not been well for a "couple of days" and was "taking a break from the campaign".
He said: "Of course Diane is somebody that works extremely hard and represents her community very well and I have to say has received totally unfair levels of attack and abuse not just recently - over many years."
Prime Minister Theresa May said: "How Jeremy Corbyn manages his shadow cabinet is for him. I just wish Diane a speedy recovery."
Ms Brown, 57, was first appointed to Labour's shadow home affairs team when Mr Corbyn named his first frontbench team in 2015.
MP for West Ham since 2005, she is fighting the election in the ultra-safe east London seat, which she held with a majority of almost 28,000 in 2015.
She was a Labour whip under Gordon Brown and Ed Miliband, before being appointed shadow minister for communities and local government in 2013 and then shadow home office minister two years later.