Pop hunk Justin Timberlake has come to the rescue of troubled ex-love Britney Spears' career - by offering to write songs for her. The Cry Me A River singer, who is now dating Hollywood star Cameron Diaz, has offered to help Britney's flagging career after watching her suffer the heartbreak of having to cancel her tour. And now Britney - who is recovering from an injured knee - is hoping her collaborations with Timberlake will keep fans happy as she waits to reschedule her Onyx Hotel tour. A source says, "Justin is there for Britney at the moment because she has had a really tough time. "She is obviously upset about having to cancel her tour. Even though her songs are doing OK, she is worried about how letting her fans down will affect her future." An insider close to Justin adds, "Justin feels bad for her and he in a position at the moment to help. "They fell out badly when they first split up, but now they both have new partners, they have been able to rekindle a friendship."