Over the last year, Murray has struggled with a hip problem which required surgery and he attempted to return for Wimbledon earlier this month.
The Scot played two warm-up competitions at Queen’s and Eastbourne, but he suffered early defeats at both events.
He then withdrew from Wimbledon just hours before the draw was about to be made.
Murray will make another attempt to come back in Washington this week as part of his preparations for the US Open.
But it is still not clear if he will ever reach the heights of his former glory.
“You do think about ‘what if I can’t come back, what if this is the end?’ and think about what you are going to do with yourself,” he told Sky Sports.
“I have been playing tennis my whole life. This is all I have known, so it will be a big change when I do stop, but I always felt like I would be able to come back.
“It is obviously not where I would want to be ranking-wise but the good thing is, when you are up at the top of the game, it is not easy just to move up one spot.
“If I win a couple of matches here, I could move up 300, 400 spots in a week, which is nice.”
Murray is back in action at the Citi Open, a competition which also boasts Alexander Zverev and John Isner, but he is keeping his feet grounded.
“Expectations are pretty low. I have been practicing quite well,” Murray added.
“I have been competitive with all of the guys I have been playing with , I just need to try and transfer that onto the match court.
“It is a bit harder than what people think. The mental side of things is challenging but physically I am getting a bit stronger every time.
“I am hoping it won’t take too long.
“To stay healthy, that is kind of it right now.
“If I do that and get the match fitness back towards the end of the year and towards 2019 I’ll be feeling more like my old self and I’ll have a strong 2019.”