MIAMI (AFP) - Bernard Tomic's woes continued on Thursday as he pulled out of the Miami Open due to a back injury, the latest setback in a disappointing year for the Australian.
Ranked 17th in the world as recently as November, he has tumbled down the rankings to 44th.
Since a third-round Australian Open exit, the 24-year-old has lost four first-round matches to lowly ranked opponents.
The most recent setback came at Indian Wells, where he was beaten by 112th-ranked Bjorn Fratangelo of the United States.
At Acapulco in February, Tomic retired from his opening match citing "unbearable heat" and the fact that he withdrew from four ATP matches last year has led to some questioning of his attitude.
Tomic was due to face Kazakh qualifier Mikhail Kukushkin at Crandon Park on Thursday but pulled out shortly before the contest was due to begin.
Lucky loser Mikhail Youzhny of Russia took Tomic's place in the first-round contest.
World No. 41 Marcel Granollers of Spain fell 7-6 (8-6), 4-6, 6-3 to promising 62nd-ranked Croatian Borna Coric in a testing 2hr 51 min contest.
Coric tired towards the end and offered some openings to Granollers while missing three match points but was able to recover well to hold on and set up a meeting with sixth seed Dominic Thiem of Austria.
Russian 19-year-old Andrey Rublev made short work of world No. 46 Florian Mayer of Germany, winning 6-1, 6-1 in just 44 minutes. Rublev will now face a tough challenge against 2010 Miami finalist and 10th seed Tomas Berdych.