It should be a very young Araneidae, maybe Zygiella sp. Do you remember if it had an orb web extending from the silken tube seen in the second picture?
Many thanks for your help Alessandro. I'm afraid that I do not remember whether it had an orb web extending from the silken tube, but I think that you are right and that it is a Zygiella sp. as it looks very similar to this Link Regards