The former world No 1 revealed ahead of the French Open that he had been forced to rest following a second-round defeat at the US Open because of tendinitis in his left psoas muscle, which connects the spine to the femur.
Murray, who suffered a heavy first-round loss to Stan Wawrinka at Roland Garros, was due to stay in Cologne for a second tournament in a row – the bett1HULKS Championships – after he was beaten by Fernando Verdasco in his opening match in the German city on Tuesday.
The three-time Grand Slam champion, now ranked world No 115, had been drawn to face Serbia’s Danilo Petrovic.
In a message on his Facebook page, Murray said: “I’ve been dealing with tendinitis in my left psoas, which has kind of been on and off since the US Open.
“I’ve been trying to deal with it in training and the matches. Unfortunately after my match here this week it’s flared up again. I’ve been practising the last few days and trying to manage it but, after playing some points today, I decided that it was not going to be good enough to play.
“I’d like to thank the tournament for giving me the opportunity to come and play here, I’m sorry it hasn’t worked out. See you on the court soon.”
Murray could feature again this season at the Paris Masters, the final event of the regular ATP Tour season, which begins at the end of the month.
A combination of a complication from his hip resurfacing operation that sidelined him for the first two months of the year and the coronavirus-enforced hiatus to the season has seen Murray play only four tournaments this year, winning three matches.