The so-called “professional managerial class” is (1) not a class, and (2) a grouping that cuts across the proletariat and petit bourgeiosie (and is largely contained within the intelligentsia component of those classes.)

(Its basically an American-Left resurrection of the Leninist critique of the behavior of the intelligentsia, divorced from the theory in which that critique was grounded which recognized that the intelligentsia were not a genuine classes because their relation to the economy was predominantly as wage labor hired by capital–and thus proletarian–but occasionally petit bourgeois; its kind of weird that its invocation seemed to fade after the 1970s but has become popular again in the last few years.)