  In this letter we generalised the procedure of non-abelian T-duality based on
a B-shift and a sequence of formal abelian T-dualities in non-isometric
directions to 11-dimensional backgrounds. This consists of a C-shift followed
by either a formal U-duality transformation or taking a IIB section. We
investigate restrictions and applicability of the procedure and find that it
can provide supergravity solutions for the SL(5) exceptional Drinfeld algebra
only when a spectator field is present, which is consistent with examples known
in the literature.
