He was 48. The newspaper reported Causi's death on its website Sunday night and included an image of Monday's back page.
It featured a photo of Causi holding a camera with a long lens and the words "Our Eyes, Our Heart" and then below: "And our city's loss."
Causi was married with two young children. Many of New York's professional teams and several players posted messages on Twitter expressing sadness, condolences and paying tribute to him.
"Do you know how many athletes reached out when they heard he was sick?" said Stephen Lynch, Editor-in-Chief at The Post.
"Players from every team, sending thoughts, hoping he was going to be all right."
Major League Baseball called Causi a "sports photojournalist extraordinaire" and said he "brought out the best in the players and the people of our National Pastime."
Causi was a smiling and friendly fixture at venues from Yankee Stadium to Madison Square Garden and others all over the New York area.
His action shots often popped impressively on The Post's sports pages, and he was well-liked not only by media colleagues but also the famous players he chronicled.
"What a great man. So sorry to hear," tweeted Texas Rangers infielder Todd Frazier, who played for both the Yankees and Mets. (AP) INDIND