Murray reached the Wimbledon quarter-finals for a sixth straight year
The second seed clutched at his side a few times during Monday's 6-4 7-6 (7/5) 6-1 win on Centre Court, which was a worrying echo of the back troubles the endured during the claycourt season which led to him pulling out of the French Open.
After missing almost four weeks of the season, Murray returned to the tour at Queen's Club last month, winning the title, and had looked in supreme form during his first three matches at the All England Club.
Although his latest win was also straight sets, there was not the same fluency about Murray's game, with the Scot having to fight back from 5-2 down in the second set and then 5-3 down in the ensuing tie-break.
He played down worries over his fitness, though, saying: "There's no cause for concern. My back is what it is. It's felt way, way better than it was a few weeks ago.
"There's a few times on the court where you feel things. You just have to find a way of managing those issues and getting through them because a lot of guys have had problems during this slam especially.
"A lot of guys have had trainers on court and what-not. So everyone's got little niggles. You just have to manage them and get through it."
Murray retired mid-match for only the second time in his career against Marcel Granollers in Rome prior to his French Open withdrawal but, in a Wimbledon tournament that has seen more than its fair share of injury problems, only something drastic would put him out.
The second seed said: "Now that I'm playing, there's no chance I would stop unless I couldn't hold the racket."
Murray had 20 minutes of additional treatment on his body after leaving the court to try to ensure he is in prime condition for potentially three matches to come, starting with a quarter-final against Fernando Verdasco on Wednesday.
Murray said: "I need to make sure I do all the right things, like ice-bathing, having my massage, and taking care of my body.
"Obviously, a few weeks ago I missed the French Open. I don't want it to be a case of things creeping back up on me. I want to take care of my body. It's my main priority this tournament."
Centre Court was still recovering from the shock of seeing Williams eliminated by Sabine Lisicki when Murray and Youzhny walked out.
The atmosphere was flat and so was the match in its early stages, with neither player finding their best form in the first set, although Murray secured the only break of serve in the third game.
It was all a struggle, though, and that continued in the second set, with Youzhny clawing his way back from 40-0 to deuce on Murray's serve in the second game.
Having come through that, Murray played two of his best shots of the match, a half-volley drop shot and pinpoint lob, to force a break point in the following game and then topped them both with a scrambling forehand pass.
But he could not cement it as Youzhny forced two break-back points, taking the second when Murray netted a forehand, the Scot slamming his racket into his shoe.
The situation was to get worse, as a few minutes later Murray double-faulted to hand Youzhny a second successive break and a 4-2 lead.
There was a nervousness around Centre Court, which only increased when Youzhny recovered from 0-30 to win a fourth game in a row.
Murray stopped the rot by holding, and with Youzhny serving for the set he got the crowd going with a brilliant forehand down the line on the stretch.
Two break points disappeared but a third arrived and this time Murray took it with a blistering cross-court backhand, geeing the crowd up as he ran back to his chair.
The 26-year-old had a chance to break for 6-5 but Youzhny landed a forehand right in the corner to hang on.
Murray was grabbing at his hip but he hammered down an ace to force a tie-break.
It was tense, and a tame double fault from Murray to trail 4-2 did not help, but he retrieved the mini-break with a precision drop shot, skipping into the air as he willed it over the net.
A forehand wide from Youzhny gave Murray his first set point, which he took in style with a stunning backhand return. The crowd roared and Murray yelled and punched the air.
Youzhny took a medical timeout before the start of the third set for treatment to his right shoulder, and immediately threatened the Murray serve once more.
There was confusion all round as Murray made a late decision to play a ball he thought was out, appealing to the line judge and umpire in vain.
That brought up a second break point but the Scot saved it with an ace and then took advantage of a poor game from his opponent to break to love for a 2-0 lead.
Youzhny's threat had passed, and another break gave Murray a 5-1 advantage and the chance to serve for victory.
He set up a first match point with a sizzling forehand winner and put away a volley to clinch victory after two hours and 37 minutes.