Kidman and Keith Urban's relationship is reportedly under strain.
The two Australian stars tied the knot in 2006, and have daughters Sunday Rose and Faith Margaret together, but work pressures could be tearing the marriage apart.
Sources close to the couple say that because of their careers, the stars barely get to see each other at the moment.
"Tensions are reaching boiling point within their marriage. It's no secret that they're spending increasing periods apart, and Keith's close friendship with J-Lo won't have helped, especially as both Jen and Keith are returning to American Idol next season," an insider told British magazine Grazia.
Country music star Keith has sat on the judging panel for American Idol since 2013. He served as a mentor on The Voice Australia prior to that.
Nicole has been having a hard time with her film career recently, after Grace of Monaco, the big screen retelling of the love story between Grace Kelly and Prince Rainier III of Monaco, received a poor response from critics.
"Nicole's had a lot on her plate with the panning that Grace of Monaco got, and it won't be helping if she no longer feels she can lean on Keith," the insider continued.
"It's fair to say communication doesn't seem great between them, to the extent that they're decreasingly talking face-to-face. Friends are wondering whether their eighth wedding anniversary will be their last."
But friends' worries could be unfounded, as Nicole recently spoke out about how she would give up acting for love, should it ever come to that.
"I have never had to; I would, absolutely. I wouldn't even think twice about it because I would hope there is something else I can do, and I would find something else to do. I think love is the core emotion, and I have certainly existed without that in my life, and it's a very empty life," she told movies.ie.
"I have always said; when I won the Oscar [for The Hours], I went home and I didn't have that in my life. That was the most intensely lonely period of my life."
