Kelly tweeted on Friday evening: "Unfortunately I managed to break my arm yesterday @ExeterRaces. Thank you to their team as well as @page_fuller (Page Fuller) and @lucyljg (Lucy Gardner) for looking after me.
"Should be back in 4 weeks or so."
Twice successful at the Cheltenham Festival, Kelly has been a ground-breaking rider in recent seasons, becoming the first female jockey to ride a Grade One winner over jumps in Britain when Tea For Two landed the Kauto Star Novices Chase at Kempton Park in 2015.
The same combination struck gold again at Aintree in 2017, beating Cue Card by a neck in the Betway Bowl.