The frontbencher pulled out of two major election events on Tuesday due to illness amid relentless criticism from the Tories.
She stumbled through a major TV interview on Monday, when she was grilled on security measures following the London terror attack.
Labour leader Jeremy Corbyn said Abbott had not been well for a "couple of days" and was "taking a break from the campaign".
Of course Diane is somebody that works extremely hard
He said: "Of course Diane is somebody that works extremely hard and represents her community very well.
"I have to say has received totally unfair levels of attack and abuse not just recently over many years."
Asked how long she would be taking a break, Mr Corbyn replied: "I'll be talking to her later on today – she's not well at the moment."
Labour's Diane Abbott, a close ally of Jeremy Corbyn, is unwell Diane Abbott's most controversial quotes Fri, April 7, 2017
Outspoken Shadow Home Secretary, Diane Abbott holds strong opinions which does not always go down well.
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Abortion is an issue of conscience for the Labour party.
She will be temporarily replaced by Lyn Brown, the party said
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But she was replaced by Shadow Foreign Secretary Emily Thornberry.
Evening Standard editor and former Tory chancellor George Osborne tweeted: "Diane Abbott has pulled out of Evening Standard hustings.
"It's not like someone who wants to be Home Sec has much to talk about these days."
Labour frontbencher Keir Starmer this morning refused to say whether Abbott would become Home Secretary if Labour wins the election.
The Shadow Brexit Secretary told Sky News: "You know it's a question I can't answer because it's for any Prime Minister on Friday.
"It's not for me to say and I think you know that."
Ms Brown was first appointed to Labour's shadow home affairs team when Mr Corbyn named his first frontbench team in 2015.
But she was among a slew of MPs who resigned the following year following a vote of no confidence in his leadership.
The MP for West Ham said then that Labour should seek a new leader "for the good of the party and the country".
The 57-year-old is fighting tomorrow's 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 former leaders Gordon Brown and Ed Miliband.
She was appointed shadow minister for communities and local government in 2013 and then shadow home office minister two years later.