  We investigate the contribution of extended radio sources such as Centaurus
A, and Galactic supernova remnants (SNRs) to our ability to detect the
statistical $21\,\rm{cm}$ signal from the Epoch of Reionisation (EoR) with the
Murchison Widefield Array (MWA). These sources are typically ignored because
they are in highly attenuated parts of the MWA primary beam, however in
aggregate these sources have apparent flux densities of $10\,\rm{Jy}$ on
angular scales we expect to detect the $21\,\rm{cm}$ signal. We create bespoke
multi-component 2D Gaussian models for Galactic SNRs and for Centaurus A, and
simulate the visibilities for two MWA snapshot observations. We grid those
visibilities and then Fourier transform them with respect to frequency,
averaging them both spherically and cylindrically to produce the 1D and 2D
power spectra. We compare the simulated 1D power spectra to the expected
$21\,\rm{cm}$ power spectrum. We find that although these extended sources are
in highly attenuated parts of the MWA primary beam pattern, collectively they
have enough power ($\sim10^4-10^5\,\rm{mK^2}\,\it{h^{-3}} \,\rm{Mpc^{3}}$) on
EoR significant modes ($|\mathbf{k}| \leq 0.1 h \rm{Mpc}^{-1}$) to prohibit
detection of the $21\,\rm{cm}$ signal ($10^4\,\rm{mK^2}\,\it{h^{-3}}
\,\rm{Mpc^{3}}$). We find that $50-90\%$ of sources must be removed in order to
reduce leakage to a level of $10-20\%$ of the $21\,\rm{cm}$ power spectrum on
EoR significant modes. The effects of widefield extended sources will have
implications on the detectability of the $21\,\rm{cm}$ signal for the MWA and
with the future Square Kilometre Array (SKA).
