Australian waitress Courtney Webb recently alleged that she spent the night at Zayn's north London home.
Justin apparently told Yahoo! omg! UK: "I am there for him whatever he is going through - that is what buddies do. If he wants to go away and have a little trip to get away from things that is cool.
"We could go and do a weekend in Vegas and just get away from everything."
The singer, who has split from Selena Gomez, said he understood the pressure of dealing with private problems in the public eye.
"All you want is privacy but you know it isn't going to happen," he said.
Justin added: "All the One Direction guys are my buddies - but I do get along really great with Zayn.
"We hang out a lot and we have a whole bunch of common interests and find similar stuff funny. He is a really good guy."