Nadal, the winner of a record 21 Grand Slam singles titles, complained of a chest issue during his run to the final of the ATP 1000 event in Indian Wells, California last week.
Upon his arrival in Spain today, Nadal visited his medical team in Barcelona for tests which revealed "a stress fracture of the third left costal arch".
"This is not good news and I did not expect this," Nadal said in a statement sent by his team.