Complex sentence: In January 2010, he reached a then-career-high ranking of World No.4, after which del Potro had to withdraw from most of the tournaments in 2010 due to a wrist injury.
Split into simpler sentences: In January 2010, he reached a career-high ranking of World No.4. Soon after attaining this ranking, del Potro had to withdraw from most of the tournaments in 2010 due to a wrist injury.