The 23-year-old left the ITV2 reality show yesterday for "personal reasons".
It has seen been claimed Niall is 'in hiding' and won't be giving any press interviews, despite it being standard procedure for departing contestants.
Speaking on today's This Morning, Love Island fan Holly said: "It's odd that he didn't get to say goodbye.
"It feels like…alarm bells slightly ring I guess."
Phil, 56, added with a sigh: "I don't like the sound of this."
Click here to play our Love Island games – and win a £10,000 holiday for you and three friends
As they discussed the issue with last year's finalist Olivia Attwood, he added how the real reason will come out eventually whether Niall likes it or not.
He said: "I've got a feeling, no matter what it is – obviously we hope all his family are alright, his friends are OK, we hope he's OK – but if it's something else, unfortunately you can't keep a lid on these things."
The comments come after The Sun Online exclusively revealed how Niall's friends "couldn't get hold of him" after finding out about his shock exit.
One pal, who asked not to be named, told us: “We don't know what's gone on and we haven’t spoken to him so we’re in the dark.”
A second, who spoke to us close to Niall’s home in Coventry, added: “We just found out when it came on the press.
“We are as shocked as everyone else is. It's a shame as he was doing really well and was taking the show by storm.
“He is really popular as he's a lovely boy.”