Let in is fine. Remember we're talking association football here. Soccer if you prefer. I've watched enough matches to know that concede is the preferred choice by commentators and journalists. I wouldn't know in American English, but soccer doesn't seem to be that popular there.I am not an avid sports fan, and North Americans please feel free to correct me, but I doubt we'd say "concede" a goal, which would appear to be BE. I think in North America you'd be much more likely to say "allow" a goal or "let in" a goal.