Jorgensen followed up his brace of tries in his side's season-opening win over the Queensland Reds last week with another pair in the 36-13 victory over the Fijian Drua in Sydney as the Waratahs notched up back-to-back successes.
"We didn't have him for long last season and when you lose players like that it really hurts," said McKellar.
"I think the challenge is for us to make sure we get his program right with his (strength and conditioning) work and his training load so that he gets through a full Super Rugby season.
"He comes up with match-changing moments. That's the pleasing thing at the moment, is we're keeping him on the field."
Jorgensen played six times in the 2025 Super Rugby campaign prior to sustaining an ankle injury that cut his season short.
He recovered to feature for Australia in their narrow 2-1 series loss against the British and Irish Lions in July and has since signed a five-year deal with the Waratahs to fend off interest from National Rugby League clubs.
Jorgensen scored the pick of the Waratahs' tries against the Drua when, in the 37th minute, he used his foot speed and a swivel of his hips to bewilder the visitors and score in the corner, establishing a lead his side would not relinquish.
"You just shake your head," McKellar said of Jorgensen's defence-beating move. "He's beaten him in a phone booth. There's not many players who can score that try on the planet. It's a great moment. He's building a highlights reel quickly.
"I thought he did a lot of other things well. His work on our contestable kicking game helped win us the ball back and it's something we've spoken about, it was much better from him tonight.
"And then he finished one off at the end there. He's off to a good start."