Ariana Grande is ditching her signature heels for the final stretch of her tour … after suffering a painful foot injury.

Ari told fans Monday she’ll be in “cozy footwear” for her London show — and possibly Tuesday’s finale — because she’s recovering from a deep cut underneath her foot.

She says it’s not a sprain or muscular injury, but putting weight on the foot has been tough … so the heels are staying backstage.

She joked fans may notice she’s “a few inches shorter than usual” onstage … but made it clear the injury won’t keep her from performing, writing, “but please do not fret. on with the show and i am on the mend!”

The timing is certainly less than ideal … Ariana is wrapping up her 10-show run at London’s O2 Arena, with the “Eternal Sunshine Tour” scheduled to end Tuesday after nearly three months on the road.

As TMZ previously reported … Ari has also said she plans to step back from the public eye once the tour is over.