Jennifer Aniston is reportedly insecure about Justin Theroux's budding friendship with Liv Tyler.

Theroux and Tyler are currently working together in new TV show The Leftovers and the 45-year-old Friends actress is annoyed about it.

Adding on, Aniston is more upset that close friend Courteney Cox, who announced her engagement to Snow Patrol musician Johnny McDaid last month, may tie the knot before her.

"There's talk that at this rate Courteney Cox is going to be walking down the aisle before Jen, despite only having just got engaged. Jen has felt disheartened, and is said to have been pushing Justin to set a date, and even floating the idea of eloping," an insider told Grazia magazine.

"Adding to the stress is the fact that Liv is a New York native, when Justin's refusal to move to LA has been a bone of contention. Jen's said to be considering putting their LA home on the market, as they've spent so little time there."

The We're The Millers actress and Theroux, 42, announced their engagement in August 2012 after dating for 15 months. Though there were reports that the couple's relationship is on shaky grounds, the two have ignored the rumours and are still going strong with their romance.

"He's a lot more laidback than Jen, which is a quality he shares with Liv. And that's not all he and Liv have in common. They both value the simple things in life and are each eccentric in their own way, whereas Jen is very mainstream.

"There's a part of her that worries that Justin's friendship with Liv could provide things that his relationship with her just can't," the source added.