Spiegel didn't respond to People's request for comment.
Bieber, 26, has strongly denied the accusations and filed a $20 million lawsuit against the two accusers.
In the filing, his lawyers say the claims are "factually impossible, and disproven both by indisputable documentary evidence and the individuals' own admissions."
One of the women, identified as Danielle, claims Bieber assaulted her at the Four Seasons hotel in Texas in March 2014.
But according to Bieber's suit, he merely dined at the hotel's restaurant that night and did not stay there.
The star was photographed the same night with his then-girlfriend Selena Gomez, leaving a SXSW performance for a rental property where they were staying with friends.
The other woman, Kadi, claims Bieber invited her to his New York City hotel suite after the 2015 Met Gala and assaulted her around 2.30 am.
Bieber's filing claims he was "at the Met Gala after-party with dozens of witnesses" at that time.
Bieber previously wrote on Twitter that claims of sexual abuse should be taken very seriously.
"However this story is factually impossible and that is why I will be working with twitter and authorities to take legal action," he went on.
Where to get help:
• Lifeline: 0800 543 354 (available 24/7)
• Suicide Crisis Helpline: 0508 828 865 (0508 TAUTOKO) (available 24/7)
• Youth services: (06) 3555 906
• Youthline: 0800 376 633
• Kidsline: 0800 543 754 (available 24/7)
• Whatsup: 0800 942 8787 (1pm to 11pm)
• Depression helpline: 0800 111 757 (available 24/7)
• Rainbow Youth: (09) 376 4155
• CASPER Suicide Prevention
If it is an emergency and you feel like you or someone else is at risk, call 111.
If you're in danger now:
• Phone the police on 111 or ask neighbours or friends to ring for you.
• Run outside and head for where there are other people.
• Scream for help so that your neighbours can hear you.
• Take the children with you.
• Don't stop to get anything else.
• If you are being abused, remember it's not your fault. Violence is never okay.
Where to go for help or more information:
• Women's Refuge: Free national crisis line operates 24/7 - 0800 refuge or 0800 733 843 www.womensrefuge.org.nz
• Shine, free national helpline 9am-11pm every day - 0508 744 633 www.2shine.org.nz
• It's Not Ok: Information line 0800 456 450 www.areyouok.org.nz
• Shakti: Providing specialist cultural services for African, Asian and Middle Eastern women and their children. Crisis line 24/7 0800 742 584
• Ministry of Justice: www.justice.govt.nz/family-justice/domestic-violence
• National Network of Stopping Violence: www.nnsvs.org.nz
• White Ribbon: Aiming to eliminate men's violence towards women, focusing this year on sexual violence and the issue of consent.