Rihanna is apparently being watched around the clock so remains in great shape for the remainder of her tour.

The 23-year-old singer has had to cancel dates due to illness in recent weeks and is said to be extremely exhausted.

Britain's Daily Mirror newspaper now claims that the Barbadian starlet has been put under 24-hour surveillance and given a curfew by her record label ahead of this weekend's Capital Jingle Bell Ball event.

"She's filming her Loud tour DVD in December and her team is determined that she looks, acts and performs at her best," a source told the publication.

"They are currently in talks with Mariah Carey's trainer, Patricia Gay, to fly in and start training."

Rihanna apparently had a tearful exchange with her mentor Beyonc Knowles last week because she hasn't been feeling well for a while and is finding her ten-month, 101-date world tour arduous.

The pregnant singer is said to have advised Rihanna to complete her tour and then take a year off to relax to prevent burn out.

"She's just a young woman who just wants to have fun, but she was feeling pretty low," a source told British newspaper The Sun.

"It's a mix of exhaustion and stress. She's been partying hard to take her mind off things, but there are days when she wakes up and doesn't even know where she is because of the travelling. It's no wonder she is feeling down."

Rihanna has 16 more dates until her Loud tour is officially complete. Her final performance will take place in London on December 22.