Triathlon world champion Alistair Brownlee says his latest injury could seriously disrupt his title defence.
The Leeds 22-year-old is recovering from a stress fracture in his leg.
Brownlee has already missed the Sydney leg of the series and is also out of the Seoul event on 8 May. He aims to return in Spain in early June.
"If I can be back by Madrid that means I've got a pretty good chance to be a serious contender. If I can't, then the series is gone," he said.
Brownlee announced himself onto the world stage in the Spanish capital last year, beating his more experienced rivals to claim victory. Repeating that success in Washington, Austria, London and Australia secured his position as world number one.
His latest injury is his third such stress fracture he has suffered and Brownlee admits to being frustrated with his latest setback.
"I absolutely hate it. It's not so much missing the training it's just the fact you're used to doing five or six hours of activity a day and then overnight that stops," he said.
"Getting back into training has happened slowly. I had some time off before I could start swimming and then a bit more time off before starting biking and now I'm starting running."
Brownlee is hoping to reach full training in the next three to four weeks and indicated it may take another six weeks to then reach full-fitness.
The Leeds based athlete has been touted as an excellent prospect for success at the London Olympics, but he feels a lowering of expectations, following his enforced absence, could have a positive effect.
"It's a shame I've disrupted the momentum but it's kind of taken a bit of pressure off and I've got a slightly different focus to the season," he added.
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