The former world number one has not played a competitive match since Wimbledon last summer and has twice aborted comeback attempts, first at the US Open and then in Australia in January.
After the second of those he went under the knife in Melbourne and was initially very positive about his prospects.
Following a successful period in the gym, he expressed hope he would be able to return before the grass-court season and the Lawn Tennis Association created two new second-tier tournaments in Glasgow and Loughborough, partly with Murray's comeback in mind.
But the Glasgow event came and went last week without him and Murray is not on the entry list for the tournament in Loughborough, beginning on May 21.
The Scot, who turns 31 next week, has been notably quiet on social media since a flurry of activity when he returned to on-court training in France at the end of March.
He has reportedly not been seen at his training base at Wimbledon for a number of weeks, and his coach Jamie Delgado posted a picture on Twitter on Tuesday after hitting, not with Murray but Tim Henman.
Murray was on the entry list for the Fever-Tree Championships at Queen's Club, which was released on Tuesday, while he has also entered the Libema Open in Holland, starting on June 11.
But the signs now are he could well miss both, as well as potentially Wimbledon, meaning he would not have played competitive tennis for more than a year.
Murray has continued to enter tournaments, most recently the Citi Open in Washington, which starts on July 28. In an accompanying interview with the Washington Post, the three-time grand slam champion compared his recovery to the back surgery he had in 2013, saying: "This time's been harder. There's been a lot more ups and downs."
Speaking in Monte Carlo last month, Rafael Nadal gave an indication that all was not well with Murray's recovery after revealing he had spoken to his long-time friend and rival on the phone.
The world number one said: "I know how tough and frustrating it is when you work every day and you don't see the light of how to improve. But then one day trying things, trying treatments, one day things are going better, no? That's what I really hope about him because he is important, very important, for our tour."
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