The Catalan giants were unable to maintain their 100 percent start in Group D after playing out a goalless draw away to the Greek side, although the result still left Barca three points clear at the summit.
However, Valverde admits to being left frustrated after Barcelona failed to secure their progression through to the last-16.
“We tried to get to our opponents’ goal through possession, but they did a great job defensively and tried to surprise us on the counterattack, spurred on by their fans,” he said after the game.
“We had chances to win and qualify, but it wasn’t to be and we have to keep going. We have one game less.
“We only lacked a goal against an inferior team on paper, but we’ve taken a step forward, even if it’s not the one we wanted.
“We’re satisfied but not entirely so. The problem with your opponents dropping so deep is that you can only push on gradually and they can also gain momentum.
“The most difficult part of football is having to play against such withdrawn defences."
Valverde received a warm welcome from the home fans after making his return to the club he managed over two stints and added: “Tribute from Olympiakos fans? It touched me. They were very generous with me.
“They always behaved very well and had a lot of patience for me. It was exciting for me to come back here.”