Given that there are only three central defenders left from last season's first team squad, it is hard to imagine Jones and Smalling will be in direct competition too often in the early part of the season.
That will change should Van Gaal bring in new centre-backs during the transfer window, or revert to the 4-3-3 he has traditionally favoured. If it does, which of the two young Englishmen will Van Gaal prefer?
In the current set-up, they have a very complementary set of abilities, individual strengths which Van Gaal will value.
Phil Jones is very comfortable in possession, happy to carry the ball forward and looks at ease in wide positions when the centre-backs are asked to split.
He is extremely courageous—a glance at his injury record might suggest he was brave to a fault. He does a wonderful line in last-ditch challenges, and for the most part his interventions are well timed.
Van Gaal's current system is brilliant news for Jones, because the need for numbers at centre-half means he is unlikely to be shifted out of position as often. An extended spell in his natural role is likely improve his abilities.
He is far from the perfect centre-half yet. He still looks rash on occasion. He would greatly benefit from remembering that discretion can indeed be the better part of valour.
This is another way in which Van Gaal's system can benefit Jones. With three at the back there is greater cover for those moments when an apparent rush of blood to the head gets his team in trouble.
Following United's 7-0 demolition of L.A. Galaxy in July, Jones said of his new role, per Ian Ladyman of the Daily Mail Online:
You get used to a new system. This is the first time I’ve played three at the back.
Every manager has got his philosophy. We’re all pulling in the right direction and hopefully we’ll have a better season.
It’s not a massive difference to what you’re used to. You’re a defender and you’ve got to defend. We’ll keep working on it and I’m sure we’ll be ready come the start of the season.
Chris Smalling was also optimistic about his chances in the new system, speaking at a press conference on United's preseason tour, per ManUtd.com:
I probably like this system more than the traditional 4-4-2 because it gives us a lot of freedom to play and be aggressive. As a defender I’d like to think that’s my game.
Smalling invoked Van Gaal's semi-final run during the World Cup, saying:
We were very much looking forward to playing the system. We obviously saw Holland’s success in the summer and that gives us a lot of confidence that we can pick it up and do a good job.
Smalling's role in United's back three is equivalent to Ron Vlaar's with the Dutch national side. His job is to attack the ball, and his excellent timing and aerial ability are well suited to do so.
He also has the pace to act as the last line of defence when his colleagues are in trouble.
Smalling's distribution is not as good as Jones'. Last season, Jones completed an average 88.3 percent of his passes to Smalling's 82.7 percent. Smalling is comfortable enough on the ball, however, and made an average of 0.6 dribbles per game to Jones' 0.3.
Smalling was often deployed as a right-back, a role which lends itself to higher numbers of dribbles, but he has shown himself to be comfortable carrying the ball out of the centre of defence too.
The truth of the matter is that both players are currently vital to United. They have the potential to develop further, working as part of Van Gaal's back three.
Should they come into direct competition, Van Gaal would have to decide between Smalling's solidity and aerial presence, and Jones' bombast and better distribution. Jones may win out in the end; after all, Sir Alex Ferguson once said he could be "our best ever player," per Sky Sports.
However, for now United's first team is better off for a system that incorporates them both.
All stats per WhoScored.com