Youngsters Nico Gonzalez and Abde Ezzalzouli were on target for Barca, but Osasuna fought back at El Sadar with goals from David Garcia and Chimy Avila.
Barca are now without a win in three games under new coach Xavi Hernandez and, after being knocked out of the Champions League in midweek, have slipped to eighth in the league table.
“Like Xavi said [after the defeat to Bayern Munich on Wednesday], a new era is starting and it’s vital we start picking up points in LaLiga,” Pique told Movistar.
“We’re adrift [of the top four] and the more points we can make up in the coming weeks, the better. We competed today, but the result was a huge shame.
“Now it’s about winning, winning and winning. We are in a critical situation and it’s urgent that we get back to winning ways.”
Barca, who will play in the Europa League in the new year for the first time in 17 years, are now five points off fourth-placed Atletico Madrid and 15 behind leaders Real Madrid, who meet in the Madrid derby later on Sunday (stream live on ESPN+ at 3 p.m. ET)..
Pressed on whether simply obtaining a top-four place, and qualification to next season’s Champions League, is now the target, Pique refused to set long-term goals,
“The objective now is to think about the next game,” he added. “The only objectives are short-term. Long-term, it’s good for the club that the youngsters are playing regularly, but we have to think short-term.”
Coach Xavi said the performances of teenagers Gavi, 17, Nico, 19, and Abde, also 19, was both positive and negative for Barca.
Gavi, already a full international with Spain, set up the first goal for Nico, with Moroccan winger Abde crowning another impressive display with his first goal for the club after a break led by Ousmane Dembele.
“Abde, Gavi and Nico were extraordinary,” Xavi said in his post-game news conference. “We’re lucky with the contribution the youngsters are making. It was a great effort from the whole team, but it’s the youngsters making the difference — and that’s difficult to digest.
“I think that’s positive and negative. It is a positive for the future but also a negative because such young players can’t always be the standout performers. We have to demand more from everyone.”
Barca — who were missing seven players against Osasuna, including Jordi Alba, Pedri, Ansu Fati and Memphis Depay — now travel to Saudi Arabia for the Maradona Cup on Tuesday against Boca Juniors, with their next competitive game in LaLiga at Camp Nou on Saturday vs. Elche.