Celebrity Big Brother lost more than two million viewers on Saturday after its launch show attracted 5.2 million.
Greer and fellow contestants entered Big Brother on Thursday
The latest series of the Channel 4 reality show drew 21.8% of the available TV audience on Thursday.
But ratings dropped to 2.9 million on Saturday, a 12.6% audience share, as the show fell behind BBC One drama Sea of Souls and ITV1's Ultimate Force.
Celebrity Big Brother drew 3.5 million viewers on Sunday. A mystery ninth contestant enters the house on Monday.
Happy Mondays dancer Bez, author Germaine Greer, actors Brigitte Nielsen and Jeremy Edwards and racing pundit John McCririck are among those competing for a £50,000 prize for their chosen charity.
On Monday bookmaker William Hill tipped McCririck to be the first evicted, with Edwards their favourite to win the 18-day contest.
It is Channel 4's third series of Celebrity Big Brother, which attracted 12.3 million viewers to its first series finale in 2001, won by comedian Jack Dee.
Former Holby City actor Edwards has been tipped as a favourite
Ex-Take That star Mark Owen won its second series in 2003, its climax watched by more than six million viewers.
Later that year former Channel 4 chief executive Mark Thompson - now the BBC's director general - said there would be no more series of Celebrity Big Brother, saying it would no longer be interesting.
But a change of management at the network saw the reality show reprieved.