The midfielder, sidelined since early January with a thigh problem, could make his first-team comeback against Everton this afternoon.
Shelvey is a contender to replace the injured Sean Longstaff in Rafa Benitez's starting XI.
The 27-year-old – who played 60 minutes for the club's Under-23s last week –has spoken about his recovery in today's matchday programme.
Asked what the last few months had been like, Shelvey said: "Torture, to be honest. It's hard watching the team play and not being able to help.
"We should have nipped it in the bud early doors, but it wasn't to be.
"I had numerous trips to Barcelona to get injections to try to sort it out. The doc said if I did it one more time I would have had to have surgery on it, so it was time to shut down, get it right and come back stronger for the end of the season."
The injury dates back to last summer, when Shelvey was playing through the pain barrier.
"It started pre-season," said Shelvey. "I was taking injections to play the games, because I'm one of those people who always just wants to play football, and obviously I just play through the pain barrier.
"But every time I was kicking a football, it felt like someone was stabbing me in the leg. The pain was unbearable in the end.
"I needed to rest and recover and start to repair it."
Rafa Benitez was asked about Shelvey's readiness to play at his pre-match press conference.
United's manager said: "Yes, but there's fit and there's match fit. He has to play games."