Emma Raducanu has revealed she has ‘got to get stronger’ after blaming a stiff back on her third round exit at Indian Wells.

The 19-year-old was defeated 6-7, 6-4, 7-5 by Croatia’s Petra Martić at the WTA 1000 event.

It was a frustrating match for Raducanu, who let Martić back into the clash after leading 5-4 in the third set. She has now blamed the loss on fitness issues.

"I think it's just part of not playing and having so much stop-start and having five, six days to prepare for matches and then playing at that intensity,” Raducanu said.

"It was a tough one not being able to serve full out so I was having to work so hard just to hold. I've just got to get stronger.

"I've had it [stiff back] for the last few days, just a product of training hard and probably the last match was pretty intense too and it didn't settle down.

"When you are crossing your fingers to hold serve every time, it's tough. I couldn't really drive up and I was kind of struggling to turn and reach. The margins were so small."

Raducanu has been blighted by fitness issues since her improbable victory at the US Open in September.

The star became the first ever qualifier, male or female, to earn a Grand Slam title. She won 10 games in a row without dropping a set, and became the first female British tennis player to claim a major since Virginia Wade in 1977.

Raducanu was subsequently beaten in the quarter-finals of the Transylvania Open due to illness, before severe blistering on her right hand led to defeat in the second round of the Australian Open.

She then retired from her first-round match at the Guadalajara Open last month with a hip injury, only just recovering in time for Indian Wells. Despite these issues, Raducanu is expected to be fit in time for the Miami Open later this month.

In Raducanu’s absence, compatriot Harriet Dart has embarked on a brilliant run at Indian Wells, coming through two rounds of qualifying to enter the main draw and reach the last 16.

She earned the biggest win of her career in the second round, coming back from one set down to defeat world number 18 Elina Svitolina 2-6 6-3 6-3.

The 25-year-old then overcame Kaia Kanepi 7-6, 6-3 to set up a clash with Australian Open finalist Madison Keys. The match is scheduled to take place this evening.

Dart was ranked outside of the world’s top 120 going into Indian Wells, but she is now projected at world number 99. She could rise even higher up the standings if she beats Keys.