CYAD Celyad Oncology SA

UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

WASHINGTON, D.C. 20549

FORM 6-K/A

REPORT OF FOREIGN PRIVATE ISSUER

PURSUANT TO RULE 13a-16 OR 15d-16

UNDER THE SECURITIES EXCHANGE ACT OF 1934

For the Month of September 2019

Commission File Number: 001-37452

CELYAD SA

(Translation of registrant’s name into English)

Rue Edouard Belin 2

1435 Mont-Saint-Guibert, Belgium

(Address of principal executive offices)

Indicate by check mark whether the registrant files or will file annual reports under cover of Form 20-F or Form 40-F.

Form 20-F  ☒            Form 40-F  ☐

Indicate by check mark if the registrant is submitting the Form 6-K in paper as permitted by Regulation S-T Rule 101(b)(1):  ☐

Indicate by check mark if the registrant is submitting the Form 6-K in paper as permitted by Regulation S-T Rule 101(b)(7):  ☐

Celyad SA

On August 22, 2019, Celyad SA (the “Company”) furnished its interim results for the six months ended June 30, 2019 (the “Interim Results”) on a Report on Form 6-K (the “Form 6-K”). This Amendment (the “Amendment”) to the Form 6-K is being furnished solely to provide eXtensible Business Reporting Language tagging for the financial statements included in the Interim Results. There are no other changes to the Form 6-K.

Exhibits 101.INS, 101.SCH, 101.CAL, 101.DEF, 101.LAB and 101.PRE furnished with this Amendment are hereby incorporated by reference into the Company’s Registration Statements on Forms F-3 (File No. 333-220285) and S-8 (File No. 333-220737).