  We show that massive young star clusters may be possible candidates that can
accelerate Galactic cosmic rays (CRs) in the range of $10^7\hbox{--}10^9$ GeV
(between the `knee' and `ankle'). Various plausible scenarios such as
acceleration at the wind termination shock (WTS), supernova shocks inside these
young star clusters, etc. have been proposed,since it is difficult to
accelerate particles up to the $10^7\hbox{--}10^9$ GeV range in the standard
paradigm of CR acceleration in supernova remnants. We consider a model for the
production of different nuclei in CRs from massive stellar winds using the
observed distribution of young star clusters in the Galactic plane. We present
a detailed calculation of CR transport in the Galaxy, taking into account the
effect of diffusion, interaction losses during propagation, and particle
re-acceleration by old supernova remnants to determine the all-particle CR
spectrum. Using the maximum energy estimate from the Hillas criterion, we argue
that a young massive star cluster can accelerate protons up to a few tens of
PeV. Upon comparison with the observed data, our model requires a CR source
spectrum with an exponential cutoff of $5\times 10^7 Z$ GeV ($50\,Z$~PeV) from
these clusters together with a cosmic-ray injection fraction of $\sim 5\%$ of
the wind kinetic energy. We discuss the possibility of achieving these
requirements in star clusters, and the associated uncertainties, in the context
of considering star clusters as the natural accelerator of the `second
component' of Galactic cosmic rays.
