Andrew Flintoff (groin), Craig White (side) and Ashley Giles (wrist) are due to link up with Hussain's men in Adelaide next week and then continue their rehabilitation work.
But England hoped Vaughan's injury problems were behind him - until he started complaining of soreness in his knee following the Sydney Test.
The selectors kept him out of the first batch of triangular tournament one-day matches in December so he could work on strengthening the joint and also recover from a damaged shoulder, which has hampered his throwing and prevented him bowling his offbreaks.
"When we rested Michael earlier in this tournament, that was why," added Hussain. "He was fine going into the Melbourne Test. Given a week off, like he might get this week, hopefully the knee will improve again.
"Vaughan's an absolute 'gun' player for England and in great form. But with the World Cup only a month away we have to treat both him and Harmison carefully."
Barring major problems, it seems certain Hussain and Co will aim to nurse Vaughan through the next couple of months in the hope he can have an impact on the World Cup. But, sooner or later, more keyhole surgery may be the only option.
"There's no real break after the World Cup but his knee needs to be thoroughly looked at," Hussain said. "With the amount of cricket going on you can't always be pencilling in two or three weeks off.
"Eventually, someone will have to have a good look at his knee and try to get him on the park for both forms of cricket."
England will be desperate for Vaughan to not only start the World Cup but also play a full part throughout the event.
"With the World Cup, you've got to look to play your best side all the time and look to win every game," said Hussain. "Ideally, we should have been playing our best side all through this triangular tournament but the injury situation hasn't let us do that.
"We'll be patient but we've been struggling around Australia this winter carrying injured people and I don't really want to struggle around the World Cup carrying injured people."
Just for the moment, though, the host nation have almost as much cause for concern.
Australia looked a pale imitation of World Cup holders when they lost heavily to Sri Lanka in Sydney yesterday, particularly in the bowling department with Shane Warne (shoulder), Jason Gillespie (elbow) and Glenn McGrath (side) were all missing.
Warne launched his comeback today by playing for Victoria in Melbourne and McGrath could return to open the attack against England tomorrow.
