Thaddeus Walter Cieslak (November 22, 1912 – May 9, 1993) was an American Major League Baseball third baseman who played for the Philadelphia Phillies in 1944.

Cieslak was one of many ballplayers who only appeared in the major leagues during World War II.

He made his major-league debut on April 18, 1944, in a home game against the Brooklyn Dodgers at Shibe Park.

In five of his games Cieslak was a left fielder, and handled 12 chances without making an error.

This biographical article relating to an American baseball third baseman is a stub.