Former world No. 3 David Ferrer, who has been a fixture in the Top 10 and the second week of Slams for the past decade, has won just three matches this season.
Following four straight first-round defeats, the 35-year-old has entered this week's ATP tournament in Estoril. Ferrer has dropped to No. 31 in the rankings.
"I do not know when it will change and if I'll get more wins and become more confident," he told Spanish press following his defeat to Kevin Anderson at Barcelona. "It's been a lot of kilometers, I don't recover the way I used to and I'm not the same physically. Now, I have to train differently."
Ferrer, who reached the final of the French Open in 2013, has played on the ATP tour since he was a teenager and was rarely injured. He now says he has a chronic tendon problem.
"Personally I am good, there is no frustration," he said. "I've had a regular career, I haven't had a major injury and I would have signed to have a career like I had had and to reach the age of 35 like I am now."
The Spaniard has also reached two semifinals at the Grand Slams, at the Australian Open and the U.S. Open, and has 696 wins and 339 losses, including 26 titles.
Ferrer wants to lift his game as much as he can for the French Open, and then assess his physical level.