Mohamed Salah played for Egypt in an international friendly against Algeria on Monday
Health officials said hundreds of people were killed by an explosion at a crowded hospital in Gaza City on Tuesday night.
Salah, 31, said humanitarian aid to Gaza must be allowed "immediately".
"There has been too much violence, heartbreak and brutality," he said.
Palestinian officials say the blast at Al-Ahli Arab Hospital was caused by an Israeli air strike.
But the Israeli military say it was the result of a failed rocket launch by Palestinian Islamic Jihad - an accusation the militant group rejected.
Israeli warplanes and artillery have been bombarding Gaza in response to an unprecedented attack on Israel on 7 October by the main Palestinian militant group, Hamas, which killed 1,400 people.
More than 3,000 people have been reported killed by strikes on Gaza.
Salah described the scenes from the hospital as "horrifying".
"The people of Gaza need food, water and medical supplies urgently," Salah said in a video posted on X.
"All lives are sacred and must be protected. The massacres need to stop. Families are being torn apart.
"I am calling on the world leaders to come together to prevent further slaughter of innocent souls.
"Humanity must prevail."
The Algerian football federation said on Wednesday it is suspending all football competitions and matches "in solidarity with the Palestinian people".
The governing body had previously agreed to host the Palestine national team's forthcoming football matches following a request from the Palestinian FA.
-- Courtesy of BBC Sport