The Spaniard was beaten in straight sets on Centre Court on Monday by the Belgian world number 135.
"There were not a lot of good things for me," Nadal told BBC Sport. "I tried my best all the time I had my chances but I did not make it.
"It is difficult to adapt your game on grass. The only thing I can do is congratulate my opponent. It is not a tragedy I lost, it is sport."
The defeat marks the first time that Nadal has been beaten in the opening round of a Grand Slam since he turned professional in 2001.