The telly host, who left ITV1's Dancing On Ice to front the new reality series, apparently feels like Jessie J is taking all of the limelight.
"Holly took this job thinking it'd be the bigger gig of her career yet. But so far, it's not going to plan," a source says. "She can’t help thinking she's being totally overshadowed by Jessie."
According to Star magazine, tension between Jessie and Holly on set has grown behind the scenes.
"After watching the first episode, Holly joke that she came across like a bit part. She is worried that she cannot possibly compete with Jessie’s powerful on-screen presence," the insider told the publication.
They added: "Holly is no diva, but behind the scenes there are mumblings that there are problems between her and Jessie."
Holly's lack of screen time on the show hasn't gone unnoticed by fans.
Many viewers took to forums to question whether the blonde beauty had even been cut from the series completely, after featuring for just a few minutes in the opening audition episode.
One said: "I blinked and missed her."
Another complained: "Seriously she's been on screen for about 5 of the past 35 minutes! Why is Reggie getting all the glory?! I love Holly!"
And one viewer joked: "She left DOI for this, lol. Hope she gets some more screen time soon or it was a bad move."
Holly's co-host Reggie however insisted recently that the show wasn't about him or Holly.
He said: "Holly and I aren’t the stars of the show – the artists and the coaches are and we’re merely here to guide them.”
The Voice UK continues this Saturday night on BBC One.