Manchester United’s sprawling, tree-lined training ground in suburban Carrington, England, is, by all accounts, among the best facilities in soccer.
Behind its well-guarded walls are 14 fields, a gymnasium, indoor running tracks, squash and basketball courts, underwater treadmills, a sauna, seven first-team locker rooms and a $33-million medical facility with a hospital wing and a sports-science department.
Yet it’s abandoned every summer when Manchester United hits the road for its preseason training camp, arguably the most important three weeks of the season.
Last year the team toured China. The two summers before that it visited the U.S.
This month United is...