Muhammad Ali -- Pneumonia Lands Champ in Hospital

Muhammad Ali is in a hospital battling pneumonia -- but doctors expect him to make a full recovery.

72-year-old Ali was admitted to an undisclosed hospital early Saturday morning ... according to a rep for the boxing legend. The rep says it's a mild case of pneumonia which doctors caught early -- so he's not expected to have a very long hospital stay.

Earlier this month ... TMZ Sports got pics of "The Greatest" hanging with Snoop Dogg at Nevada's high school championship game. Snoop's son and Ali's grandson were teammates at Bishop Gorman high.