Vettori strained ligaments in his right knee against Pakistan and missed New Zealand's final two group games, including last Friday's heavy defeat by Sri Lanka.
The all-rounder, 32, told reporters yesterday that he "should be fine" for today's quarter-final. Wearing strapping on his knee, Vettori later took part in a training session at Sher-e-Bangla National Stadium, missing a warm-up game of rugby but staying behind afterward to practise his bowling with Nathan McCullum.
New Zealand are also set to be boosted by the return of Kyle Mills, the pace bowler, after a calf strain, and Vettori said Brendon McCullum, the opening batsman and wicketkeeper, will continue to play through a knee problem.
Today's game could be Vettori's last as captain of the one-day side. The veteran of 270 ODIs intends to give up the captaincy of the one-day and Twenty20 sides after the tournament, and he is reportedly considering retiring from limited-overs internationals altogether.
The left-arm spinner's return could be crucial to New Zealand. In beating the West Indies at the same ground on Wednesday, Pakistan's three spinners combined to take eight for 64, and South Africa's slow bowlers were central in bowling out Bangladesh for 78 on Saturday.
Vettori was more concerned that his hit-and-miss batsmen deliver today. "They will be the key to our success," he said. "We played our best game against Pakistan when our batting fired, we got a guy through to a hundred, and had a couple of crucial partnerships. We've been at our worst when those things haven't happened."
Graeme Smith, the South Africa captain, is not underestimating New Zealand and he said: "New Zealand have always been a very street-smart team and they've always played well to their abilities and they've always got a lot of guys that can contribute so you need to play well to beat them."
South Africa sailed through the group stages with wins over the West Indies, Netherlands, Ireland, Bangladesh and India, while they lost to England in a low-scoring game. Smith said the Proteas wanted to continue their dominance, but hinted it would be a tight game.
"It's two quality teams, anyone from here can win the World Cup and that's what makes this tournament exciting," he said. "They have some power batters, some guys that really take the game to you. From a bowling point of view, they always take the pace off the ball, they have a lot of guys that can change the pace."
But Smith was confident South Africa could reach the last four.
"We're in a great place at the moment. We've had 10 days in Bangladesh so we've had to keep ourselves busy a little bit outside training sessions, just keep things a bit fresh in the mind," he said.