The midfield enforcer has passed a medical and will sign a one-month contract once formalities have been completed in France later this week.
The 34-year-old has impressed on trial with Blues in recent weeks and Lee Clark has now moved to add the former Senegal international to his ranks.
Diop earned a reputation as one of Europe’s most powerful central midfielders during a successful six-year stint in the Barclays Premier League with Fulham and Portsmouth, gaining a 2008 FA Cup winners’ medal with the latter.
After a year with AEK Athens, in which he lifted the 2011 Greek Cup, Diop returned to England last season and played his part in West Ham United’s promotion via the npower Championship play-offs.
The powerhouse called time on his international career in 2008 having represented quarter-finalists Senegal at the 2002 FIFA World Cup and at four African Cup of Nations finals.