The Australia goalkeeper sustained the injury during Saturday's 2-0 defeat at Swansea and saw a specialist consultant on Tuesday night.
Schwarzer has now been diagnosed with a compression injury to his thoracic spine and will be unavailable for between four and six weeks.
As a result of losing Schwarzer for a spell, Martin Jol has invoked a loan agreement clause that sees England squad member David Stockdale return from a spell with Ipswich.
The injury ruled Schwarzer out of this evening's vital Europa League Group K clash with Odense at Craven Cottage.
The 39-year-old was expected to be replaced by Philippines international Neil Etheridge, making his first-team debut aged 21.
Etheridge began his career with SW6 rivals Chelsea and penned a contract extension with Fulham until 2013 in the summer.
Source: FOOTYMAD
