Britain's Andy Murray says he will continue to have physical problems until he has stopped growing.
Murray took a two sets to one lead against Monfils before succumbing
The 19-year-old, who suffered cramp at Wimbledon last year, was hampered by a back problem in a five-set defeat to Gael Monfils at the French Open.
"I had an X-ray and it showed the bones aren't fully grown. That's why my back gets sore and that's why I get cramp," Murray told Five Live Sport.
"I've worked hard on getting it stronger. I'll be fitter next year."
Murray took a two sets to one lead over fellow 19-year-old Monfils but he was already restricted by the back problem by then and the Frenchman hit back.
The Scot said he considered pulling out, but was worried about the media reaction after his well-documented physical problems in the last year.
"I knew it would be 'Andy Murray's injury problems, Andy Murray doesn't fight'," he said.
"I thought it was best to finish the match. I think I showed I want to win every match but unfortunately I couldn't finish the way I wanted to."
However, Murray did have encouraging news on his search for a coach to replace Mark Petchey.
"I'm not going to give you any names but there is one guy I would really like to coach me," he said.
"It's always difficult with the best coaches because they all have things they're tied in to. It make more time than I would like but I'm getting there."