Excitation-energy spectra of C-11 nuclei near the eta'-meson production threshold have been measured by missing-mass spectroscopy using the C-12(p,d) reaction. A carbon target has been irradiated with a 2.5 GeV proton beam supplied by the synchrotron SIS-18 at GSI to produce eta'-meson bound states in C-11 nuclei. Deuterons emitted at 0 degrees in the reaction have been momentum analyzed by the fragment separator (FRS), used as a high-resolution spectrometer. No distinct structure due to the formation of eta'-mesic states is observed although a high statistical sensitivity is achieved in the experimental spectra. Upper limits on the formation cross sections of eta'-mesic states are determined, and thereby a constraint imposed on the eta'-nucleus interaction is discussed.