Webber had leg surgery last week
The Australian, who on Monday was without crutches but visibly limping as the new Red Bull was unveiled at Jerez, last Thursday had surgery to remove a pin from the injury, sustained in November in a high-speed mountain cycling crash.
He told reporters that, despite the surgery, his more badly shattered tibia injury is still carrying the medallions of his initial Tasmania operation — a 10-inch rod, made of expensive titanium to reduce weight.
"I've still got one in there," Webber, 32, said at the Spanish test circuit.
"It has to stay in there for 18 months and I am now trying to build up my leg muscles," he revealed last weekend to Britain's News of the World.
Webber will try to drive the new RB5 on Wednesday, with teammate Sebastian Vettel taking up driving duties on the first two days.
He said that while he would struggle at present to complete the FIA's mandatory 7-second test to climb out of the cockpit and replace the steering-wheel, he will be able to do it as necessary in Australia.
"We were close last week and then we had that little bit of surgery which put us back a little bit," said Webber.
"The thing (leg) will be functional for Melbourne for 90 minutes. I can't run a marathon but luckily I don't need to."