Lily Collins flashed her taut midriff as she led the arrivals attending the Calvin Klein show during New York Fashion Week on Friday.
The actress, 36, was joined by models Iris Law and Emily Ratajkowski at the event which took place at The Brant Foundation.
She wore a sequinned crop top which was paired with a matching midi skirt and silver strappy heels.
Iris looked as chic as ever as she went braless in a 90s style slip dress with a mesh insert.
The model, 24, layered over a matching trench coat and topped her outfit off with a pair of quirky heels.
Meanwhile, Emily opted for a semi-sheer knitted dress with dramatic dropped arm holes and a highneck.
The Sports Illustrated star shielded her eyes with stylish oval-shaped sunglasses and completed her look with pointed toe boots.
Also in attendance was Anna Wintour and Naomi Watts who posed for photos outside the venue.
But it was Collins' slim physique - particularly her abs - that caused the most conversation, with fans expressing concern for her.
'Lily....EAT SOMETHING!!!!' one concerned netizen rote.
'Please Lily, I mean this sincerely, get help,' another posted.
'Was she always this thin? I don't normally see her in crop tops so I didn't realize. She's beautiful but I hope she is okay,' one wrote.
'Wow! Too skinny!' one wrote with a shocked face emojji.
'Somebody give her a cheeseburger!' another posted.
'Why... why.... I hope she is well!!' another wrote.
Collins previously suffered from eating disorders as a teenager and opened up about the struggle in her 2017 memoir, Unfiltered: No Shame, No Regrets, Just Me.
The actress revealed she was left terrified that she 'had ruined her chances of having kids' after her eating disorder had took hold, according to an excerpt obtained by The Times.
Lily's outing comes after she was met with furious backlash from fans after failing to acknowledge the Emily In Paris director who passed away on set this month.
The actress announced that the filming for season five had come to a close in an Instagram update and shared a montage of behind-the-scenes pictures with her co-star, Ashley Park.
Fans, however, found the post to be in bad taste after the show's assistant director Diego Borella, 47, collapsed while filming one of the show's final scenes last Thursday in Venice's Hotel Danieli.
While medics were called to the scene, they were unable to save the director, whose cause of death was later revealed to be a heart attack.
Lily wrote: ‘And that’s another wrap on @emilyinparis… Here's to five seasons of friendship turned sisterhood – Venice, Paris, Rome, anywhere is home with you by my side.
'Incredibly grateful for our Emily family and so extremely proud of what we all created together this year. Arrivederci ’til December 18!… '
'Doesn’t this seem a little tasteless and tacky? An assistant director died just 3 days ago on set?!'; 'No mention of the guy that passed?,' fans commented.
'RIP Diego Borella. Looking forward to the new series but this poor guy deserves a mention.'
It is understood that following the tragedy, filming for Emily in Paris was temporarily halted.
Borella was born in Venice in 1978 and was an accomplished director and writer, who trained in cities across the world including Rome, London and New York.
According to his social media, he has successfully published fairy tales, haikus and plays.
Spanish newspaper El Mundo reports Borella was pronounced dead at 7.30pm after resuscitation attempts failed.
