Emma Raducanu struggled with her conditioning as she lost her third-round match at Indian Wells while competing with a stiff back.
The reigning US Open champion won the first set against Petra Martic on a tie-break but went on to lose 6-7 (3-7) 6-4 7-5.
Raducanu, 19, has won just four matches in the last six months, and fitness issues have blighted the early stages of her career.
