Billie Piper, who has been at the centre of speculation that she is not well enough to appear on stage in the West End, has come out fighting, saying: "I'm doing really well."

The 24-year-old Doctor Who star has faced rumours that she could not cope with the emotionally demanding role in Treats.

She collapsed shortly before going on stage for a preview performance last week. She has also been spotted crying at a café close to her north London home and being comforted by ex-husband Chris Evans.

Last night Evans was in the audience at the Garrick Theatre to see Piper in a preview before the official opening on Thursday.

As she left the stage door with boyfriend and co-star 28-year-old Laurence Fox, Piper told the Evening Standard: "I am doing really well. It is going well and I'm really pleased."

She thanked Evans for his support saying: "It was really good having Chris here - I could hear him laughing. Bless him for being supportive."

The former pop star missed the first preview night after she was taken to hospital nine days ago with an illness believed to be a recurrence of haemorrhaging cystitis.

The condition caused her to collapse in 2000 when the bladder infection-spread to her kidneys. She was also rumoured to be a "nervous wreck" over her demanding role in the Christopher Hamilton play, in which she plays a journalist torn between two men.

But after seeing her on stage, Evans was full of praise. As he left the theatre he said: "I thought Bill was brilliant. When she cried, I cried."

Producer Bill Kenwright, who last week took the unprecedented decision to postpone the official opening for a week to give Piper a chance to recover and prepare herself to face the critics, also praised her performance.

He said: "This kid is the hardest working, most energetic lady in the industry."

The audience also gave Piper their backing.

Greg Wilton, 27, said: "I have not personally thought she was that wonderful in any of her TV performances, but she outshone any of those roles this evening. I thought she was really good and certainly held her own.

"She performed like a professional actress and there was no sense of her going through any personal problems-they weren't brought to the stage."

Jasmine Walker, 39, from Stratford, said: "She was really good. I came to see her really and was worried after everything I had read about her in the papers, but she certainly performed tonight." Friend Mandy Thomas, 41, added: "It is certainly worth watching, although it is a very emotional play. It can't be easy to act something like that, but I thought she did a very good job."

Kenwright's team are understood to have drawn up contingency plans in case Piper cannot fulfil her threemonth commitment to the play. A spokesman for the producer said: "Billie is under an enormous amount of pressure at the moment."