The white woman, who is in her 30s, was said to have been left in “shock” after she was set upon by a trio “dressed all in black” as she walked to work.
“She had three Asian girls behind her chanting the Koran, ‘Allah’,” Karrien Stevens, the operations manager of Little Diamonds nursery in Wanstead, east London, told the Press Association.
“They pulled her to the ground, punched her, kicked her. One of them pulled out a knife and cut her arm from her wrist to her elbow.”
Police were called to the scene on the corner of Wanstead High Street and Hermon Hill at 9.36am on Wednesday.
A Metropolitan Police spokesman said: “Counter-terror officers are aware of the incident but it is not being treated as terrorism at this stage.”
Ms Stevens said her colleague had just left Wanstead station when she was set upon by the three women less than 10 minutes’ walk from the nursery at around 9.30am.
She said the victim did not know her attackers, who fled the scene when a passer-by intervened.
The victim, who was not wearing a uniform, was left “shocked” by the ordeal, which lasted around 10 minutes, and Ms Stevens insisted the attack was not related to the nursery.
“There is no reason for it whatsoever,” she said.
“She is shaken up, she’s emotionally a bit of a wreck, they did scare her, but she is OK, she is a strong staff member.”
Speaking of the victim’s injuries, she added: “She was in tears and she had a cut right up her arm.
“Her stomach was hurting, she had marks all over her, her hair was pulled out.”
A Met spokesman said she was taken to an east London hospital as a precaution with a slash wound, but her injuries were not life-threatening.
“The suspects fled the scene prior to police arrival in an unknown direction. No arrests have been made,” he added.
Paul Ashmore, 31, a mixing and mastering engineer in South Woodford, said his fiancee and child were held on lockdown at Wanstead Church School, a 30-second walk from the incident.
He said his fiancee called him to say the school was not allowing anyone to leave “because there was a stabbing outside”, and added the police did not know “where the persons who did it were”.
They were initially told it was gang-related, he said.
“My instant thought was to collect my fiancee and kid and get them to safety not knowing the full extent of what was happening.
“But I was thinking the worst.
“I instantly, after what has been happening regarding terrorists, thought the worst and informed her I will drive up to collect them,” Mr Ashmore said.