  We consider a stationary spherically symmetric monopole like solution with a
finite energy density in a pure quantum chromodynamics (QCD). The solution can
be treated as a static Wu-Yang monopole dressed in time dependent field
corresponding to off-diagonal gluons. We have proved that such a stationary
monopole field represents a background vacuum field of the QCD effective action
which is stable against quantum gluon fluctuations. This resolves a
long-standing problem of existence of a stable vacuum field in QCD and opens a
new avenue towards microscopic theory of the vacuum.
