Unai Emery had little time for negativity after Arsenal's Europa League humbling at the hands of Rennes as he attempts to lift the spirits in a crucial showdown with Manchester United.

The 10-man Gunners suffered a demoralising 3-1 defeat in the last-16 first leg at Roazhon Park on Thursday, leaving an uphill task in the upcoming return tie.

The timing of the defeat was not exactly ideal given the in-form Red Devils travel to Emirates Stadium on Sunday fresh off one of the greatest turnarounds in Champions League history against Paris Saint-Germain, with a 3-1 triumph in Paris booking a quarter-final berth.

But Gunners head coach Emery, recalling an encounter with one of his squad, explained that he wants only positive vibes ahead of a crucial juncture in Arsenal's season.

"I want the players to help me with big positive energy," he said. 

"One player was worse than me, more down than me, and I said to him, 'Let's speak tomorrow as you are more sad than me'. 

"I want to listen to players with positive energy. I want to hear them say, 'We can do it on Sunday'.

"In the hours after a match like that, it's not easy for me. But I came back the next morning with a big spirit, with a big confidence for Sunday first and also for this week. 

"I try to enjoy each day. In training, preparing for the match, even in defeat – I try! I am looking forward to seeing our reaction."

Defeat against old foes United could be potentially fatal to Arsenal's hopes in an increasingly heated battle in the top four, which has been bunched up further following Tottenham's loss of domestic form.

Should Ole Gunnar Solskjaer's side head back to Manchester victorious, Arsenal would be four points off the Champions League spots with eight games to play.

With their other avenue to the Champions League, winning the Europa League, increasingly uncertain after the Rennes humiliation, there is little room left for error.

But for Emery it is all about emphasising the idea of positive energy.

"Our target is to play in the Champions League and we know it is not easy," he added. 

"We have two possibilities even if we know it is going to be difficult. With this responsibility, the players are optimists. 

"We can come with positive spirit and do it. I want to find positive energy."