Barca lost 2-0 at the Estadio Ramon Sanchez-Pizjuan.
Koeman said afterwards, "We have to analyse the game. There are a lot of games before the next match.
"There has been a lot of wear and tear. We have to try to play and win in the second leg.
"There is hope, although the tie is complicated. But this team are capable of anything at home."
"There is always a doubt about penalties," Koeman stated.
"Everyone told me it was a penalty. They made fouls, but clever fouls.
"They defended very well. They are a strong team. They are a great team with a great squad.
"We are in good form, we fought. We played well, but we played against a great team, and a very physical team.
"We had chances. There is VAR, but I think there is a penalty."