Novak Djokovic is concerned about Andy Murray slipping on the grass on his return at the Fever-Tree Championships but said the mental challenge will be his biggest to overcome.
Murray has not played since Wimbledon last year, but the three-time grand slam champion will make his long-awaited comeback against Nick Kyrgios in the first round at Queen's Club next week.
The Briton underwent hip surgery in January and Djokovic - who will also start his grass-court season at the same event - said it is not just a physical test the former world number one will face when he returns.
Djokovic, who has also been hampered by injuries, said: "He needs that support [from the Queen's crowd]. He needs people to back him up, to be behind him and show him that he was missed.
"I know how that feels. Having a couple of weeks at home, these are the events where he will give 100 per cent to try to get out on the court.
"He has been absent for longer than I have. I don't know how painful it is still, or not, for him to move around.
"But I think the biggest challenge will always be mental. In my situation that was the case. How to get it out of your head, understand that it's behind you, that you're fine now, that you're healthy and you can focus on your game rather than thinking 50 per cent of the time about whether or not something can happen.
"Does it hurt me? Does it not hurt me? Am I imagining things? Is it real? Is it not real? Then 50 per cent of the time you are thinking about your tactics and what you have to execute.
"If you don't have mental clarity on the court, especially on grass where everything happens very quickly, it's very difficult to play."
The Serbian added: "I don't know the state of his hips. But the one thing that could be a bit dangerous is slipping on the grass.
"That's something that is very unpredictable and grass is always this kind of surface where one wrong footing can make something go wrong, especially in the hips.
"I just hope for his sake that doesn't happen."
|Sissoko: Dembele criticism overblown|
|Thibodeau discusses Butler trade: We thought this was the best deal for us|
|Acuna, Ohtani win rookie of the year awards|
|LeBron James on Lakers’ early season struggles: ‘I almost cracked’|
|Welbeck has successful second operation on broken ankle|
|UEFA warns FFP cases can be reopened based on ´new information´|
|Foakes to keep England place for second Test|
|WATCH: Rooney looking sharp in England training return|
|Mbappe: Money in football is truly indecent|
|Djokovic back to brilliant best as Isner is beaten|
|Celta Vigo replace Mohamed with Cardoso after Real Madrid defeat|
|Joshua intrigued by Usyk, says Hearn|
|Ibrahimovic beats Rooney to MLS Newcomer award|
|Rams WR Kupp out for season with torn ACL|
|Sturridge denies ever gambling on football following FA charge|
|Koeman understands De Ligt´s Eredivisie frustrations|
|Jimmy Butler trade: 76ers acquire Timberwolves star in blockbuster deal|
|´Improve your attitude´ - Deschamps issues Dembele warning|
|Sturridge charged with misconduct over alleged breach of betting rules|
|Saints sign Marshall following Bryant injury|
|Mendy suffers knee injury, leaves France squad with Lacazette|
|Zverev beats Cilic in error-strewn London battle|
|Rafinha replaces injured Casemiro in Brazil squad|
|´One-dimensional´ Australia batsmen need work before World Cup - Finch|
|Mancini keen to work with ´incredibly gifted´ Tonali|
|Italian manager of the year Allegri targets long Juve stay|
|Injured Lee departs as Wales prepare squad for Tonga|
|Conte content to wait until June for coaching return|
|Etzebeth set to return, Whiteley a doubt for Scotland Test|
|In-form Verstappen does not need distractions from 2019 challenge|
|FA asks Guardiola to explain Manchester derby referee comments|
|LaLiga MVP Messi hopes the division stays wide open|
|Murray and Henshaw out of All Blacks Test|
|Injured Man Utd duo Pogba and Martial drop out of France squad|
|Modric cannot always be the best - Dalic|
|Very troubling times - LeBron James alarmed by gun violence|
|Bayern confirm Ribery ´altercation´ with reporter|
|Madrid hit by injuries to Nacho and Casemiro|
|Record-breaking Mushfiqur torments Zimbabwe|
|Spartak Moscow appoint Oleg Kononov|
|Rooney predicts ´exciting time´ after being named in MLS Best XI|
|Former England call-up Graham replaces Thomson in Scotland squad|
|Slater and Thurston among Queensland greats to join Maroons staff|
|Rapana set for six months out after shoulder surgery|
|Alves determined to play in the Premier League|
|Rockets GM denies Anthony will be waived|
|Monaco´s plight not Henry´s fault - Silva|
|It´s like the FBI came - River assistant unable to talk to Gallardo during final|
|Norman says Washington home crowds ´just don´t really care´|
|Bucks beat Nuggets to finish gruelling schedule stretch|
|Madrid ´very happy´ with Solari, says Butragueno|
|Titans stun Patriots, Browns upset Falcons|
|Browns´ Chubb relishes record-breaking performance: It definitely is very special|
|MLS Review: Red Bulls, Atlanta to meet in conference finals|
|Neymar wants more from perfect PSG|
|Higuain is feeling a lot of pressure – Gattuso|
|I didn´t insult anyone, says apologetic Higuain|
|Allegri delighted with Juventus response|
|Kyle Busch wins at Phoenix as Harvick, Truex qualify for Championship 4|
|WATCH: Highlights of thrilling Boca-River Copa Libertadores final|
|PSG coach Tuchel demands more despite Monaco thrashing|
|Boca missed too many chances, rues Schelotto|
|Solari remains tight-lipped on Real Madrid future|
|Hamilton not surprised by Verstappen-Ocon collision|
|Ronaldo fires Juventus to Serie A record|
|Higuain did nothing serious - Ronaldo hopes Milan striker avoids ban|
|Solari completes perfect Real Madrid audition with fourth straight win|
|Verstappen ordered to do public service after Ocon scuffle|
|Nishikori stuns out-of-sorts Federer|
|Fitzgerald overtakes Owens in career receiving yards|