England manager Thomas Tuchel has made the decision to hold key training sessions at England's tournament base in Kansas City, rather than in Mexico, due to concerns over potential spying by other teams.
The decision is partly to avoid the most severe effects of altitude sickness, which typically occur between three and nine days after arrival, but also to prevent valuable insight into England's team shape and selection from being obtained by spies.
England have screened-off training pitches and have a heavy security presence provided by the local police in Kansas City, and intend to return there for the build-up to their later knockout matches if they progress past their last-16 clash.
The issue of spying in football has been highlighted in recent years, with Southampton ejected from the Championship play-off final for admitting to spying on Middlesbrough's training sessions, and Canada's women's national team given a six-point deduction for using a drone to watch New Zealand train at the Olympic games two years ago.
England also have concerns that the location of their hotel in Mexico will be leaked and targeted by Mexico supporters before their match, following an incident where Ecuador's players were kept awake by home fans outside their hotel in Mexico City.
Ecuador have submitted a complaint to Fifa, stating that such conduct is "in stark contrast to the principles of fair play, equity, and unity that a World Cup should embody".
England's team hotel in Mexico is expected to have roadblocks around its perimeter to try and guard against pre-game disruption, amid growing concerns over fan behaviour at the World Cup.
