The Wimbledon champion decided earlier this week not to play in a Great Britain tie for the first time in more than three years because of this summer’s demanding schedule.
But he promised to travel to Serbia and was at the Tasmajdan Stadium for the team’s afternoon practice session.
It was obvious Murray was itching to join in, but Smith described his mere presence as “a big boost”.
The absence of Murray and world No 1 Novak Djokovic has turned what could have been one of the Davis Cup’s biggest recent occasions into a distinctly average quarter-final.
Beverley’s Kyle Edmund takes on the role of British No 1 for the first time and will face former top 10 player Janko Tipsarevic in the first rubber today.
The second match will be between James Ward and Serbia’s Dusan Lajovic.
Edmund’s only previous Davis Cup experience came in last year’s final when he won the first two sets against Belgian No 1 David Goffin before losing in five.
The 21-year-old insisted he will not be fazed by the occasion, saying: “I approach it as another match, I do the same routines, the same mindset. Nothing will change. I see this as another good opportunity for me.”
Tipsarevic did not play at all in 2014 after twice undergoing surgery to remove benign tumours from his left heel and then spent another spell on the sidelines with knee problems.
The 32-year-old, now ranked world No 405, said: “I didn’t play Davis Cup for a long time so I’m making up for lost time. I feel a lot of happiness being able to play all three days.
“As the weeks are going by I feel that I’m only missing matches. Over two years out and three surgeries left me with a lot of doubts and insecurities but I feel I’m playing better and better.”
Tipsarevic admitted his knowledge of Edmund, the highest ranked player in the tie at 67, is minimal, saying: “I don’t know much because he broke through in the two years when I was basically in hibernation.
“I know he can play on clay. He’s definitely not your cliche British player that can only play on grass or hard courts.
“He’s like 12 years old, very, very young, and he has a bright future. This is a chance for him to say, ‘Okay, this is not only an Andy Murray team, I can also beat some good players’.”
Ward had been due to play in a grass-court tournament in Newport, Rhode Island this week but made the switch to clay after Smith drafted him into the team in place of Dan Evans.
The Londoner’s ranking has slumped to 240 but he has had some of his most eye-catching wins in Davis Cup.
Ward said: “I’m happy to be here. I love playing for my country, I always have. It’s generally brought the best out of me so hopefully it happens again this weekend.”
Saturday’s doubles will pit Jamie Murray and Dom Inglot against Tipsarevic and Nenad Zimonjic, although nominations can change up until an hour before play, with the reverse singles taking place on Sunday.
Two potential curveballs are the weather, with rain forecast for all three days, and the temporary clay court.
Inglot said: “It does cut up a little bit, it gives you some weird bounces occasionally, but that’s tennis.”