The 21-year-old star has missed few public appearances and had appeared exhausted has worried his fans, band mates and his fiancee Perrie Edwards, reported Contactmusic.
"Zayn is stressed out and sick of his life being in the spotlight. He isn't sleeping well and seems exhausted," a source said.
The English-Irish boy band are about to go on another world tour and Perrie is worried about Malik.
"She has asked the other boys to keep an eye on him. They are concerned for him too and regularly let him know they are there to talk should he need them," added the source.