Just looking at some criticisms of his defending, especially in the Champions League this season, but he's expected to do both attacking and defending in Barca's system and he doesn't have a lot of cover behind him and has to run all the way back as well.
One Barca supporter said:
"Put Semedo is a system where he has a proper winger in front of him or in a system where midfielders and CBs can actually run and defend and he would be a truly elite RB."
Seems his weakness is his 1 on 1 defending and his crossing is weak. Those won't be as much of an issue for us as he'll have plenty of support behind him and Traore/Neto in front of him.