The troubled singer was rushed to hospital last Saturday for scans after fears she had a return attack of the disease emphysema - which she developed and was treated for in June this year.
Amy – who is still battling drug addiction – was visited by a doctor at her London home last Thursday but was rushed to The London Clinic after her condition worsened.
The centre is the same place she has previously undergone treatment for her drug problems.
A friend said: "Amy is in hospital being checked out for a chest infection. She is not back in rehab. She should be fine and is expected to return home soon."
Amy, 25, was worryingly thin and had yellow teeth as she was admitted to the hospital. The scans she was given were precautionary measures to check emphysema had not returned.
Amy is currently working on her new album, which she has said she wants to have ready for the time her husband, Blake Fielder-Civil, is released from jail at the end of this year. He is being held on counts of attempting to pervert the course of justice and grievous bodily harm.
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