  Yukawa couplings of the first quark generation are notoriously difficult to
constrain due to their small values within the Standard Model. Here we propose
Higgs off-shell production, with the Higgs boson decaying to four leptons, as a
probe of the up- and down-quark Yukawa couplings. Using kinematic discriminants
similar to the ones employed in the Higgs width measurements we find that the
down (up) Yukawa coupling can be constrained to a factor of 156 (260) times its
Standard Model value at the high-luminosity LHC assuming only experimental
systematic uncertainties. Off-shell Higgs production hence provides better
sensitivity to the first-generation quark Yukawa couplings with respect to
other probes such as Higgs+jet or Higgs pair production.
