The mysterious medical condition which caused Eminem to cancel all dates on his European tour earlier this week was yesterday revealed to be an addiction to sleeping pills.

The rap star's management put out a statement confirming that "Marshall Mathers, aka Eminem, is in the hospital under doctors' care. He's being treated for dependency on sleep medication."

On Tuesday, the Detroit artist's European Anger Management tour, due to run from September 1 to 17 and expected to earn about £10m, was called off. Four dates in Britain and Ireland were among those cancelled.

The singer cited exhaustion and "other medical issues" and his managers responded to rumours that the Grammy award-winning musician was ill by saying he wanted to spend more time with his eight-year-old daughter, Haile.

The news that Eminem is in a clinic being treated for addiction is likely to fuel speculation about his future. For several months, rumours have circulated that he is to quit performing and concentrate on producing new talent.

But the rapper, who turns 33 in October, is still the number one selling male artist in the world, although sales have dipped below the heights of the Marshall Mathers LP, which sold 19 million copies worldwide.

Eminem's latest offering, Encore, was a worldwide No 1, selling 11m copies globally, including 1.2m copies in the UK.

"I'd be surprised if this was the end of Eminem as a recording artist, but if you call your most recent two records The Eminem Show and Encore, you've got to expect it marks the end of some kind of chapter for him," said Julian Marshall from New Musical Express magazine.

"It's not out of the question that Eminem may spend the next couple of years involved in other projects - for example, following Dr Dre and producing up and coming rappers; looking at new acting roles; or getting more involved with the record label side of things, like Jay-Z did when he announced he was retiring.

"Fortunately for Eminem, he's successful enough to do what he wants, when he wants. A few years out of the public eye would only make it more exciting when he returns."

In recent years, Eminem has followed in the footsteps of Dr Dre, his mentor, a former rapper with NWA and now a highly successful producer. Eminem has been producing younger acts for several years, especially the group D12, whom he calls his proteges and who would have supported him on the UK tour, as well as artists Obie Trice and Stat Quo.

The singer has also crossed over into acting; winning critical acclaim for the semi-autobiographical film 8 Mile.

So some industry pundits are keen to point out that, with falling album sales, Eminem may be ready to hang up his microphone.

Hattie Collins, editor of urban music magazine RWD recently told the Independent: "I see him going into production and just doing the odd guest spot on a track, causing a commotion when he does. Hip hop tends to be a young person's game with people looking to who is hottest and freshest."

Proof, a rapper who is Eminem's right-hand man onstage, also recently said: "Em has definitely gotten to the level where he feels like he's accomplished everything he can accomplish in rap. He wants to kick back and get into the producing thing. Why not bow out while you're on top?"

The singer's reply to rumours of retirement was: "I know that I'm not gonna be rapping forever, I know that much. As long as I feel like I got the energy in me to do it and the spirit, and I can do it, I'm gonna do it."

Gennaro Castaldo from HMV said: "While he may not be in the place he was three or four years ago, he has been following to an extent in Dr Dre's footsteps.

"He may have had a bit of a setback, but he is still incredibly well placed and he could take his career any way he wants to go. It could well be that he feels he has achieved everything he possibly can and he is looking to apply his talents to other things.

"I think he has been so busy and under a lot of pressure that he has been talking about stepping back, but it is difficult to believe he will walk away. This is an opportunity for him to back off a bit - but you can bet he will come back bigger and better than before.

"The latest news about being in rehab just adds to the mythology of an icon anyway - you can't be in rock'n'roll without the odd addiction and affliction."