Alexi Lalas -- United States soccer legend -- wholeheartedly believes Christian Pulisic could be the greatest soccer player to ever rock the red, white, and blue ... but, there's an IF.
IF ... Christian stays healthy, Lalas tells TMZ Sports.
"We have yet to see Christian Pulisic at the highest level from an international perspective, play in a World Cup. Knock on wood he's there in November and December. And, knock on wood he's healthy because unfortunately he has a propensity to get injured and he is a little bit fragile," Lalas says.