Chelsea agreed a fee with Bolton last month, but have yet to conclude personal terms to bring the England international to Stamford Bridge.
Blues boss Andre Villas-Boas previously revealed that the two parties were 'miles apart' and that had prompted speculation Cahill was reconsidering the chance to move to West London.
Reports also suggested that Premier League champions Manchester United were ready to make a late bid to hijack the deal, while Tottenham have held a long-term interest in Cahill.
However, the centre-half is now poised to finalise his departure from the Reebok Stadium, where he is out of contract at the end of the season.
Cahill's expected arrival at Chelsea will boost Villas-Boas' options at the back after Brazil international Alex handed in a transfer request at the start of December.
Villas-Boas is also weighing up whether to add one further player to his squad during the January transfer window after allowing Nicolas Anelka to move to China.