The 26-year-old actor has played coy about his relationship status after being romantically linked to the 20-year-old actress earlier this month, but he admits her caring personality has tugged at his heartstrings.
When asked about the blonde beauty, he told Access Hollywood: ''She's really sweet. She's a sweetheart.''
The stars were spotted looking cosy as they took in a Los Angeles Lakers basketball game earlier this month.
However, Zac claims he's unsure if the pair are actually dating but insists he's not looking to romance anyone else.
Quizzed if he's off the market now, Zac quipped: ''I don't know, I'm not really sure I'm in the market ... I'm not investing. My money's out!''
Meanwhile, the heartthrob, who sought treatment for cocaine addiction twice last year, recently admitted he's in a ''great place'' after conquering his demons in rehab.
He said earlier this year: ''I'm so happy. I feel like I'm in a great place and I'm glad that I'm really here to share this moment with everybody and be present for all of it.
''It was an interesting year. I learned so many things. So much. The best part of it was being able to reflect upon that experience and realise how much I have learned about myself and the kind of man I want to be.''