We studied how an additional layer of the high T-C superconductor YBCO affects the magneto-transport across a LSMO/Alq(3)/Co spin-valve structure. We found that up to a thickness of at least 10 nm the YBCO layer on top of LSMO hardly changes the spin-valve effect, since the device resistance still depends on the relative orientation of the LSMO and Co magnetization. The spin-valve effect persists even when the superconducting YBCO layer acts as bottom electrode, with no spin-polarized current injected from LSMO into YBCO. This highlights that the charge carriers of a thin YBCO layer on top of LSMO are strongly spin- polarized, most likely due to a magnetic proximity effect involving a transfer of spin-polarized electrons from LSMO to YBCO. Evidence for a strongly underdoped state of the YBCO layers close to the interface with LSMO is indeed obtained from the dI/dV curves in zero magnetic field which reveal a pseudogap persisting well above T-C.