"We have to rest, work harder, and then on Sunday come back and have a good game," Gabriel told the club's website (www.arsenal.com).
"We just need to be calm. We have to work hard and focus on putting in a good performance (against Manchester United)," he added.
The Gunners have lost their opening two group matches in the Champions League and are bottom of their group, six points behind leaders Bayern Munich, who they have to play twice.
Gabriel said he was confident the Gunners can advance from the Champions League group stage for a 16th straight season.
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"We can still qualify. We have a very strong team, with some very good players. We now have to try to win the remaining matches in the group," the 24-year-old Brazilian said.
(Reporting by Shravanth Vijayakumar in Bengaluru; editing by Sudipto Ganguly)
