Countrywide said it expected its first half earnings to be around £20m lower in 2018 compared to the same period last year.
The market in the first half of 2018 “has continued to be subdued” and the company has experienced longer transaction cycles, the property giant said.
Countrywide’s focus is now on building up its sales pipeline by the end of 2018.
The firm is looking to investors to raise fresh funds to reduce the company’s debts by around half.
The share price fell to around 59p following the news, and has now more than halved over the past year from 167p.
Former chief executive Alison Platt resigned from Countrywide in January, as the firm was forced to offer another profit warning.
She has been replaced by Peter Long, previously a non-executive chairman, who is acting as executive chairman.
Competitor Foxtons announced a 65% drop in profits earlier this year, blaming a slowing London market.