A source reportedly tells CNN that police are concerned about unexplained injuries to Bobbi Kristina and have their eye on Nick.
Nick and Bobbi Kristina (who never legally married, contrary to early reports) were reportedly having trouble in their relationship leading up to the hospitalization.
Last year, Nick tweeted a series of erratic messages, seeming to address his relationship with Bobbi Kristina and her aunt Pat Houston, who has a protective order keeping Nick away from her immediate family.
Bobbi Kristina's hospitalization came just days before the third anniversary of her mother Whitney Houston's death on Feb. 11, 2012. Whitney passed away the day before the 2012 GRAMMYs and the music icon's 21-year-old daughter was on everyone's minds over GRAMMY weekend.
"I'm heartbroken that the Houston family is feeling such pain again," Whitney's mentor Clive Davis told ET at the Beverly Hilton Hotel. "I've been in touch with Pat and offering my support, solace and prayers. The family really requests privacy at this very trying time, and certainly I'm going to respect it and I'm sure everybody else will too."