The Gunners were smashed 4-0 by Liverpool before the international break on the back of another defeat away to Stoke.
Since that humiliation at Anfield, Arsenal have sold Alex Oxlade-Chamberlain to the Reds and failed to sign any more new players in August.
Arsene Wenger and his stars are already coming in for criticism and they must improve when they welcome Bournemouth to the Emirates tomorrow.
Spanish defender Monreal reckons Arsenal must step up their performances to stand any chance of competing for the league crown this term.
The 31-year-old said: “Obviously [the Liverpool game] was really difficult for us because we didn't expect to lose as we did.
"You can play against Liverpool away and lose this game because they are a good team, a strong team with good players, but we can't play as we played.
"We need to improve a lot, our target is to win the Premier League and obviously we can't win it if we keep playing like we did against Liverpool.
"Now we have to improve and on Saturday we have the next opportunity to get three points, so I hope the team is okay and we can win, get the three points and get confidence."
Bournemouth travel to north London having lost their opening three league fixtures but the pressure will be squarely on Arsenal tomorrow.
Monreal insists whatever the outcome is it will not spell the end of Arsenal's title hopes.
He added: “Honestly, it is too soon to speak about if we can or we can't [win the Premier League].
"We have played three games and we have only three points, that is six less than Manchester United at this moment but we are only thinking about playing Bournemouth and winning this game and keep looking forward."
