"So not to go on the court today, it's the biggest disappointment I have had."
John Isner was another casualty after pulling out of his clash with France's Adrian Mannarino just two games into his second round game.
Isner, who won the longest match in the history of the tournament against Nicolas Mahut in 2010, suffered a leg injury while serving early on.
"I just went to serve, and it was as I landed on my left leg, like I have done 20 million times playing this game. I just felt this sharp pain," 18th seed Isner told reporters.
"It just grabbed really badly and I knew I was in serious trouble then. I knew at that point it was not likely I was going to be able to play."
There was also bad news for 10th seed Cilic, who had hoped to reach the later stages of the tournament following his run to the final at the Queen's Club last week.
The Croatian had hoped to face France's Kenny de Schepper before withdrawing with a knee injury, while Radek Stepanek was forced to retire at 6-2 5-3 down to Poland's Jerzy Janowicz after pulling his left hamstring.