Duchamp studied non-Euclidean Geometries (Fig.11) far more extensively than any other artist and his scientific inspiration resides clearly on 19th century. However in some of his notes on the 4th dimension one feels Relativity Theory is present:

Gravity generate in horizontal and vertical in space3 […] We always reduce the experience of gravity to a self perceived sensation, imagined or real, felt internally near the stomach.

Duchamp, 1966, White Box (page 99)

Even if Duchamp never read any of Einstein’s ideas, nor shared enough scientific methods to get to the same conclusions, after reading this note one can’t think of anything else but Einstein Equivalence Principle. I must emphasize these quotes about gravity are contextualized within fourth dimension in both the White and the Green Box:

-Regime of Gravity-
Ministry of coincidences
Department (or better):
Regime of Coincidence
Ministry of gravity

Duchamp, Green Box

There are a few other concepts Duchamp outlines in his notes that can be easily connected to Einstein’s Relativity such as the idea of movement related to the fourth dimension and the change of a moving object’s shape:

Playfulness of Duchamp’s new physics is a demonstration of the basic principle of a non-Euclidean geometry that rejects Euclid’s assumption of the indeformability of figures in movement

Henderson, 1983, page 132

Linda Henderson explains that the scientific influence that made Duchamp write these ideas were Reimann (and other 19th century mathematicians). These were also Einstein references when he assumed Space -Time was curved and that an object goes thinner and thinner the faster it moves.