The Gunners take on Manchester United on Sunday in what is sure to be a pivotal game for both sides.
The Gunners were beaten 3-2 at the Emirates on Tuesday evening in their second shock Champions League defeat of the campaign, having already come unstuck against Dinamo Zagreb in the opening round of fixtures.
Their hopes of qualifying for the latter stages of the competition are now hanging by a thread, with many questioning Arsene Wenger and his players for their performances in Europe so far.
They are not out yet, though, and Gabriel says the focus must be on winning their remaining games and pushing through to the last 16.
“It was a complicated night [against Olympiakos],” he told arsenal.com.
“The three goals were our own fault but 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.”
Arsenal must remain calm for Manchester United clash
Arsenal now host Manchester United on Sunday in what is sure to be a big game for both sides, despite it being early in the campaign.
United have started well, currently sitting top of the Premier League table with 16 points from a possible 21, with a defeat to Swansea City and a draw with Newcastle United representing the only blots on their copybook.
They are in fine form having won their last three league games, as well as securing victories over Ipswich and Wolfsburg in League Cup and Champions League competition, and are sure to be confident of getting all three points against the Gunners.
And Gabriel says Wenger's men must remain calm ahead of a potentially pivotal clash.
“We just need to be calm. We have to work hard and focus on putting in a good performance [against Manchester United],” he added.
“We only have ourselves to blame for conceding them and now we have to rest, work harder, and then on Sunday come back and have a good game.”