The 26-year-old Newcastle man has reportedly benefited from a summer of 'personal training.'
The Magpies forward struggled desperately for fitness last term but has undergone a summer of work and could therefore be in line to give McClaren what neither Alan Pardew nor John Carver ever had at their disposal.
Indeed, the Chronicle report: 'Steve McClaren has also been boosted by the news Siem de Jong is likely to be ready to start the season after a summer of personal training.'
Like a new signing?
The old cliche - one McClaren may well use numerous times should De Jong come good next campaign.
Despite flashes of promise, the former Ajax forward's first season on Tyneside may as well have not happened. Those flashes, though, demonstrated De Jong's reading of the game and creativity. Should he stay fit, he'll provide an undoubtedly strong addition to the Newcastle side.
But can he last the distance?
Naturally, however, doubts will remain over whether the 26-year-old can really chip in for a whole season at St James' Park. The Dutchman suffered multiple injury problems last term and many of them were simply out of his control.
If De Jong can contribute with five goals or assists next term instead of just five appearances, it will be a major improvement. But what will fans realistically want from a man who clearly has the ability to produce - just not necessarily the ability to keep playing regularly?