This is the problem. The worry is he's just a medium-sized fish in a small pond and perhaps he isn't rated by the top clubs.I've never seen him play bit find it very odd that he stayed with Sporting last summer if he was that good.
He's also done very little at International level which is a lower standard than the PL.
With much less time and space and a higher standard of goalkeeper in the PL, he may struggle.
All of the above, along with the fact that he only hit big numbers last year, which is quite late, concerns me. The best players tend to leave Portugal at a younger age.