Jack, the world's best full-back at his peak and once voted the world's best player, admits that he was finding the going increasingly heavy earlier this season.
'It was the hardest job I'd ever had by a long way,' he said. It looked that way, as well, with his own immaculate reputation as a full-back suffering from his need to be everywhere else on the field, organising other aspects of play and fighting fires as they broke out in a fragile front line of defence.
Enter Andy Gregory last month and Jack could once more concentrate on doing what he does best. Salford have gained not one inspirational veteran, but, in effect, two.
'I'm enjoying playing full-back again, which is something I hadn't really enjoyed in the same way for years,' Jack said.
'I don't have to run around organising the side any more. I leave all that to Andy; he knows exactly what's required.'
Gregory's expertise and his known long-term aspiration to coach could, however, have been interpreted by the present incumbent as a possible threat.
Jack only took up the reins of his first coaching job last summer and by mid-November Salford's record of just two wins in 10 league matches had given him an uncomfortable baptism.
'But I've never seen Andy as a threat,' he insisted. 'Certainly not as long as we're winning. Andy and I work tremendously well together, but I'm not going to be at Salford forever and, after that, good luck to him.'
Good luck is what Gregory has brought Salford. Five more league victories have lifted them clear of the relegation zone and Jack sees their progress into the Regal Trophy semi-finals, at the expense of Leeds, Gregory's last club, Batley and Hull as a bonus.
Like the Welsh rugby union convert, Richard Webster, Gregory was signed on the initiative of the Salford chairman, John Wilkinson, rather than that of Jack.
Another circumstance that could make you paranoid, perhaps, but Jack took the precaution of ascertaining that the new signing was not only of the same generation, but of the same mind.
'Although I'd played against Andy many times, I didn't know him. I didn't know what to expect of him. So I phoned him up and I found he really was as keen as mustard - and that was before any terms had been agreed.
'It's not so much a matter of age as whether you've still got your enthusiasm. I'm 32 as well and I'm still pretty enthusiastic and Andy's the same.'
Jack is eager to emphasise that Salford's recent improvement has not been a one-man operation, however.
'There's no doubt that he brings the best out of other players, but we didn't buy him to make the tackles and that's the big thing that's improved.'
All his forwards, Jack says, deserve credit for that, including his fellow-Australian, Chris Tauro, who has overcome a slow start to emerge as a genuinely damaging second-row.
'And I wish someone would tell me what Paul Forber has to do to play for Great Britain,' he said. 'I haven't seen a second-row in better form recently and that includes the ones they've got at Wigan.'
Jack should be a good judge of what is required for Test rugby. Capped 20 times during five years as Australia's first choice, he was the epitome of the modern full-back, rock- solid under the high kick, a ferocious cover-tackler and an enthusiastic and penetrative counter-attacker.
Salford saw him in his prime during a short spell with the club six years ago and moved smartly to lure him from his other English side, Sheffield Eagles, in the summer after they had sacked their previous coach, Kevin Tamati.
Jack makes no secret of seeing Salford as a possible route into coaching in the Winfield Cup in Australia. It would not be a surprise at some future date to see him re- united with the Balmain club where he spent most of his Australian career, but which he left, voicing stinging criticisms of their coach, the former Wallabies supremo Alan Jones, 18 months ago.
In the meantime there is much work to be done at Salford, with the banishment of the permanent spectre of relegation a higher priority than cup competitions, however good for morale and cash flow they might be.
One decision already made is that, after this season, Jack will do that work as a non-playing coach. 'Playing and coaching is too much of a job for one man,' he said. 'I'm enjoying playing again, but you should try to go out somewhere near the top.'
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