Conor Townsend accepted Albion’s performance at St. Mary’s Stadium was “very disappointing”.
The Baggies fell to a 2-0 defeat after a first-half strike from Moussa Djenepo and an Oriol Romeu volley midway through the second half.
And Townsend admits Albion must improve when they return after the international break.
“The lads are disappointed and we all know we can and should be doing better than that,” said Townsend.
“In previous games we’ve started well, but we didn’t do that today and that’s down to all of us on the pitch. We need to improve on that.
“We’ve let ourselves down with the first-half performance. The second half was a lot better but we need to capitalise when we’re on top in the game and the second goal takes the wind out of our sails a little bit.
“We know we can compete in this league. We didn’t manage to do that this afternoon but we’ve got to dust ourselves off and move on.
“We’ve got the international break now and will be working really hard in training as we have been. We’re all determined to turn it around.”