Cara Delevingne Surfaces in Paris, Incognito Amid Health Concerns

Cara Delevingne has popped up halfway around the world all by herself and sorta undercover -- this as her inner circle has grown increasingly concerned about her health.

The model touched down Monday in Paris, where she was cruising through Charles de Gaulle Airport ... wearing a face mask, a beanie and sunglasses. She appeared to be rolling solo, with her face buried in her phone and not a whole lot of luggage on hand either.

We know there are some fashion events happening in and around Europe right now -- including in neighboring Italy -- but it's unclear what CD is doing there this week.

What we do know ... her friends and loved ones have expressed serious reservations about her state of being lately, with sources telling us Cara is in a bad way -- needing both rehab and mental health treatment for issues that seem to be consuming her these days.

Remember, she was seen looking out of sorts at Van Nuys Airport ... and her good pal, Margot Robbie, was recently seen in tears after leaving Cara's place.