World No. 6 Kei Nishikori withdrew from the Gerry Weber Open for the second straight season on Wednesday.
Nishikori forfeited his second-round match against Germany's Florian Mayer due to an injury to his oblique muscles. During his first-round match against France's Lucas Pouille on Monday, Nishikori sought treatment from the trainer between the second and third sets.
The tournament is a warm-up for Wimbledon, which starts June 27. Last year, Nishikori appeared to have trouble adjusting to grass after an impressive clay-court season and never seemed to recover the form he showed through the end of May.
He suffered a calf injury in this tournament and retired in his semifinal match. At Wimbledon, he withdrew prior to his second-round match. He then suffered a hip injury prior to the U.S. Open, where he crashed out in the first round after reaching the final in 2014.
Fellow Japanese Yuichi Sugita's second-round match against veteran Andreas Seppi was suspended due to rain with the 40th-ranked Italian leading the 102nd-ranked qualifier 4-2 in the first set.