Unai Emery believes Arsenal's result against Manchester United on Wednesday will determine whether his side have turned a corner this season.
Arsenal head to Old Trafford on a high following the feel-good factor of their scintillating performance in Sunday's 4-2 victory against Tottenham at the Emirates Stadium.
The Gunners last won at Old Trafford in the Premier League in September 2006, when Emmanuel Adebayor scored a late winner for Arsene Wenger's side in a 1-0 victory.
But Arsenal, on a 19-match unbeaten run, are three places and eight points clear of Jose Mourinho's United, who drew 2-2 at Southampton on Saturday night.
"It will be a very big challenge for us on Wednesday and it will confirm our good moment, or whether we need more," said Emery.
"It is very difficult to win there because they are a very big team with big players and have a big atmosphere pushing them, but it is an exciting match and my motivation is very big."
Arsenal's win against Spurs was overshadowed by a number of unsavoury incidents, including a banana skin being thrown in the direction of Pierre-Emerick Aubameyang as he celebrated scoring his side's opening goal, a flashpoint Emery described as "unacceptable".
Both clubs were also charged on Monday afternoon by the FA with failing to control their players after they clashed when Eric Dier equalised.
Dier's goal and Harry Kane's ensuing penalty, saw Arsenal trail at the interval, but Emery sent on Alexandre Lacazette and Aaron Ramsey in a bold double substitution, with both playing key roles in their side's turnaround.
As it stands, Ramsey is set to leave the club with his contract due to expire at the end of the season, but Emery hailed the midfielder for his contribution against Spurs.
"I want his focus only on the team, and on giving us his performances," added Emery.
"In the last matches his focus is there. We were speaking between us the coaches, and I look at him in every match. His focus is positive for us, and it helps us.
"He needs to think about his future, for his family and for him, but if he plays like he did on Sunday, it's the best for him and the best for us."
Asked if Ramsey could stay at the Emirates beyond next summer, Emery replied: "This conversation is not for today for us or for me. It's a situation that was closed one or two months ago.
"At the moment the most important thing is he's smiling, he has the commitment, the behaviour and the performances. That's the best for him and for us."
Mesut Ozil was absent against Tottenham with a back injury, and Emery hinted that the German playmaker is also likely to miss the match at Old Trafford.
Emery added: "Today he was working alone. He's had backache since last Tuesday. He couldn't play in Kiev in the Europa League or yesterday, and at the moment, I don't know if he can play in Manchester."