The invention relates to a gas injection element (10) for a system for distributing as gas inside a chamber of a fluid catalytic cracking unit. This injection element comprises a passage (14) passing right through it in a longitudinal direction (X), and —a metallic internal element (20) of which an internal surface (22) defines part of the through-passage (14) passing through in a longitudinal direction (X), —a hollow metal sleeve (30) accepting one end (20a) of the internal element (20) and attached thereto, —a hollow metal support (40) having an internal surface (42) defining the remainder of the through-passage passing through in the longitudinal direction (X), the said sleeve also being attached to one end of the support (40).