\documentclass[french]{article}
\usepackage{fontspec}
\usepackage{hyperref}
\usepackage{babel}
\addto\extrasfrench{\renewcommand{\itemautorefname}{objet \no}}
\makeatletter
\def\HyRef@testreftype#1.#2\\{%
\ltx@IfUndefined{#1autorefname}{%
\ltx@IfUndefined{#1name}{%
\HyRef@StripStar#1\\*\\\@nil{#1}%
\ltx@IfUndefined{\HyRef@name autorefname}{%
\ltx@IfUndefined{\HyRef@name name}{%
\def\HyRef@currentHtag{}%
\Hy@Warning{No autoref name for `#1'}%
}{%
\edef\HyRef@currentHtag{%
\expandafter\noexpand\csname\HyRef@name name\endcsname
\noexpand~%
}%
}%
}{%
\edef\HyRef@currentHtag{%
\expandafter\noexpand
\csname\HyRef@name autorefname\endcsname
\noexpand~%
}%
}%
}{%
\edef\HyRef@currentHtag{%
\expandafter\noexpand\csname#1name\endcsname
\noexpand~%
}%
}%
}{%
\edef\HyRef@currentHtag{%
\expandafter\noexpand\csname#1autorefname\endcsname
%\noexpand~% <---- espace "indésirable" ici !
}%
}%