Emma Raducanu knows she must "get stronger" after losing to Petra Martic in the third round of the Indian Wells Open.
Martic came from a set down to beat US Open champion Raducanu 6-7 (3-7) 6-4 7-5 on Sunday.
Teenager Raducanu has been troubled by a back injury and an issue with her hip.
The Brit says she was hampered at Indian Wells, but is confident she will be fit for the Miami Open next week.
"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,” she 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 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. I should be good for Miami, for sure."