La Paz lies at At 11,942 feet (3,640 meters) above sea level and is the highest capital city in the world.
Altitude sickness caused by breathing thin,less oxygenated air results in breathlessness, nausea, headaches, fatigue, a lack of appetite, and insomnia.
Tourist brochures give the following advice…
“If possible, try to plan your trip so that you ascend slowly. Those who have flown into La Paz from sea level tend to suffer the most. It really is much easier on the body to schedule in various stops at lower altitudes along the way. Sucre (9,214 feet/2,810 meters) or Cochabamba (8,392 feet/2,558 meters) are great places to acclimatize before making your way up to the dizzying heights of La Paz. For those who are particularly prone to altitude sickness, it’s worth considering staying in a hotel in La Paz’ upper-class Zona Sur (South Zone), which is approximately 985 feet (300 meters) lower than the city center.
Take it easy for the first couple of days. The fastest way to fall ill from sorache is to overexert yourself, so don’t try to squeeze in too much physical activity upon arrival. Instead, consider taking a taxi to the top of those steep hills, or going for a ride on the city’s famous teleférico (cable car).”
More in that vein here– for those planning a trip to La Paz after the pandemic is over.
Messi and Co are going two days or so earlier to try and beat the altitude.
Bolivia thrashed Argentina 6-1 in 2009, despite Argentina having Lionel Messi, Carlos Tevez, Javier Zanetti and Javier Mascherano in their starting XI.
So no wonder Scaloni is wary and worried.