Ole Gunnar Solskjaer continued his unbeaten start as boss after Marcus Rashford's early goal, on his 100th United appearance, sealed a ninth win in 10 matches under the Norwegian.
After that comes an FA Cup fifth-round trip to Chelsea on February 18, which is quickly followed by an Old Trafford showdown with Premier League leaders Liverpool as United do battle on three fronts this month.
However, Herrera has called for attention to remain on Fulham.
He said: "It will be a big mistake if we think further than Fulham, that's a massive game for us because Chelsea are playing (Manchester) City. Let's go game by game, because if you lose one game you regret.
"Now for Fulham, then we will think about PSG. The best way to prepare for the PSG game is to try and win away at Fulham and that's the way I think."
United have at least 16 games left this season in three different competitions - including league matches against Manchester City, Chelsea and Arsenal as well as the trip to Paris - and Herrera does not think the Red Devils will be able to extend their unbeaten run under Solskjaer until the end of the campaign.
"That is impossible, the Premier League is so tough, City is a fantastic team and they lost away at Newcastle the other day," he said.
"In the Premier League it's impossible to go unbeaten from when the manager came in, to have 25 or 30 games unbeaten."
But Herrera refused to weigh in on whether Solskjaer should get the job permanently or compare what he has done to predecessor Jose Mourinho, despite the immediate turnaround since the Portuguese was sacked in December.
He added: "We are very happy with him at the moment but it's not my decision.
"I'm not going to do comparisons. I am only going to speak about what is happening now. I'm not comparing. We are very happy with him, everyone feels free.
"We're playing with a lot of freedom, this is one of the things he is talking about every day."
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