Say was due to perform with the City of Birmingham Symphony Orchestra in Zurich, Bern, Geneva and Lucerne from Monday to Thursday.
But he says he was removed from the lineup of the planned concerts organised by the event unit of the retail company Migros.
"Officials from MIGROS cited the ideas I expressed on the Israel-Palestine tension on my social media as the reason," Say posted on his official social media account on X, formerly Twitter, on Friday.
"Everything I've written remains on my social media without any changes," he said.
A Migros spokesperson confirmed to AFP on Saturday that Say had been removed from the concert programme and replaced by Swiss pianist Louis Schwizgebel.
"The reason for this change is that Fazil Say's public statements after the terrorist attack against Israel are not defendable for Migros," the company said in a statement sent to AFP.
Hamas militants stormed into Israel from the Gaza Strip on October 7, and killed at least 1,400 people, mostly civilians who were shot, mutilated or burnt to death on the first day of the raid, according to Israeli officials.
Israel says around 1,500 Hamas fighters were killed in clashes before its army regained control of the area under attack.
More than 4,300 Palestinians, mainly civilians, have been killed across the Gaza Strip in relentless Israeli bombardments in retaliation for the attacks by the Palestinian Islamist militant group, according to the latest toll from the Hamas health ministry in Gaza.
'I am for peace'
In one of his comments, Say responded to a message posted by Turkish President Recep Tayyip Erdogan on X where he accused Israel of a rocket strike on a hospital in Gaza this week.
Israeli Prime Minister Benjamin "Netanyahu should stand trial for war crimes, genocide and massacres," Say commented.
The pianist has also criticised Hamas, saying in an October 13 video on Instagram that "nobody in the world would approve innocent people being attacked with weapons, thousands of people dying".
Say, an atheist, has previously run into trouble for his social media posts.
He was prosecuted in 2012 for Twitter posts that allegedly attacked Muslims, but acquitted of blasphemy charges by a Turkish court four years later.
"I am for peace, and all my statements were in the spirit of peace," the pianist said on Friday.
Omer Celik, spokesman for Erdogan's ruling AKP party, condemned the cancellation of Say's concerts in Europe "because of his ideas opposing Israel's inhumane attacks" on Palestinians, in a message on X on Saturday.
