The diagnosis means Nadal will almost certainly miss the ATP 500 tournaments in Dubai and Acapulco. He will be in a race to be fit for Indian Wells and Miami in early March.
Nadal, who was the defending champion in Melbourne, lost to McDonald in straight sets on Wednesday and pulled up lame reaching for a ball late in the second set. Nadal sought treatment off the court before the third set but was unable to regain ascendancy in the match, losing 6-4, 6-4, 7-5.
The iliopsoas muscle group is a deep group within the hips which connects the spine to the lower limbs, and in an effort to regain fitness, Nadal will return to Spain to receive treatment and physiotherapy.
