Pereira, who came on as a late substitute at the Britannia Stadium, said United were better in the second half, but have to be more clinical in front of goal.
The 13-time Premier League Champions have not scored more than one goal in any of their past six League matches, and their once reliable defence has begun to leak goals.
"...I think we have to look at ourselves and make sure we do better," the Brazilian told the club's website (www.manutd.com). "It's not long until the next game so I think we have to move on from this game and forget about the loss."
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The Brazil under-20 international stressed on the importance of everyone sticking together at the club as criticism of under-fire manager Louis van Gaal and the players has intensified.
Pereira praised United's travelling fans and said the players were determined to reward the supporters with victory against the visiting Blues.
"The fans are always great," he added. "They always support us and that's something we're really happy about. We have to show them (our appreciation) by picking up three points on Monday."
Van Gaal's men will take on a Chelsea side languishing in 15th place and missing suspended striker Diego Costa.
Chelsea under interim manager Guus Hiddink drew 2-2 with Watford over the weekend, dropping 10 points behind fifth-placed United after 18 games.
(Reporting by Chris Peters in Bengaluru; editing by Amlan Chakraborty)
