Novak Djokovic has warned Andy Murray he must conquer his mental demons before rediscovering his best form as the former Wimbledon champion returns from almost a year on the sidelines.
Finally recovered after hip surgery in January, Murray will play his first competitive match for 11 months when the Scot takes on Nick Kyrgios in the Queen's Club first round next week.
Murray's fitness problems, which flared up at last year's Wimbledon and featured several aborted comeback attempts, have stuck a chord with his old friend Djokovic.
The Serb was hampered by an elbow injury for much of last year and has struggled since returning after surgery.
Djokovic admits he has found it hard to feel confident on the court as he battles fears about the injury returning.
And, speaking at Queen's on Sunday, the 31-year-old told former world number one Murray not to expect an instant return to former glories.
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"I've faced this major injury issue myself. You feel the consequences mentally more than physically," Djokovic said.
"I never knew it would take so long to feel comfortable with my game.
"He has been absent for longer than me. With hips I don't know how tough it is to move around but I think the biggest challenge will be mental.
"To get it out of your head and understand you are fine, to focus on your game rather than thinking 50 percent of the time about whether the injury hurts.
"If you don't have mental clarity on the court it is very difficult to play."