A second senior sovereign debt expert has left one of the top ratings agencies, it has emerged, at a time when sovereign credit ratings are under unprecedented scrutiny in the wake of worries over the strength of the European, and in particular Greece’s, economies.

A day after Financial News revealed that Pierre Cailleteau, Moody's Investors Service's chief international economist and managing director in charge of the sovereign risk group, is leaving, it emerged that the head of Middle East sovereign ratings at rival rating agency Standard & Poor's recently left and has now taken a post at US financial services firm Citigroup.