Sienna, who has been dating the 'Notting Hill' actor since August, was reportedly left fuming after Rhys' close friend Kate Moss snubbed her offer of help before a friend's party.
The 'Layer Cake' star has now told Rhys she is fed up of trying to fit in with his circle of friends.
A source said: "Rhys has felt a huge hole in his life where his friends used to be. He thought if he could swing Kate around he would be able to get his other friends back on side. He persuaded Sienna to call Kate the night before Davinia Taylor's 30th birthday party and to ask if she needed any help.
"He told Sienna it would really help if she called Kate. She refused at first, saying it would be a really unnatural thing for her to do.
"But Rhys finally convinced Sienna. When she called and asked Kate if she needed help preparing for the party Kate laughed the offer off, patronizingly called her 'a sweetheart' and told her to have a good night."