Jamie Murray believes brother Andy can still get back to playing at the highest level and feels 2021 is shaping up to be a "huge" year for him.
Three-time Grand Slam champion Murray, 33, was forced to withdraw from next month's Australian Open after being unable to find a "workable quarantine" following a positive Covid test.
"He's done incredibly well to get to this point where he feels like he's in a position now to go out and compete against the best players in the world," Jamie told the Bunkered podcast.
"It's obviously been incredibly frustrating for him because he's had a lot of setbacks along the way. It's been very stop-start."
This year's Australian Open is the third in four years the younger Murray has missed and his ninth slam out of 13.
He was only able to play seven official matches in 2020 because of a lingering pelvic issue and the five-month coronavirus-enforced suspension of tennis. His next event is likely to be either February's Open Sud de France in Montpellier or the Rotterdam Open in March.
"Even 2020, when he was just getting back to fitness and he was just about ready to go compete in Miami, Covid hit and the tour shut down, that was another five or six-month break," Jamie said.
"So it's been difficult for him but I think he's in a good place just now. That's just the vibes I get from seeing him training and some of the matches we had in December.
"This is obviously a huge year for him. If he can stay fit, healthy, play a full calendar year and see where he's at, what his level's at, what he's able to do week in, week out on the tour. He's not had a clear run at it for two or three years, maybe even longer.
"He's still got a lot of great tennis in him. His tennis ability hasn't diminished in any way. It's just obviously whether his body can cope with the demands of the tour."