Forest take on FC Midtjylland in the second leg of their Europa League last-16 showdown on Thursday evening, needing to win by two clear goals at minimum to progress to the quarter-finals.
Forest were held to a goalless draw by Fulham last weekend, meaning they are a point behind Spurs and only out of the relegation zone by virtue of a superior goal difference to West Ham.
Such is the importance of Sunday’s match at the Tottenham Hotspur Stadium, Pereira is expected to rest a number of key players with the Spurs showdown in mind.
He said: “For me, it is a pity that I need to make decisions, to think not just about this game but the next two games. I need to think about it because it is important for the club.
“Of course, the Europa League is important for the club but the [Premier] League is very important for the club.
“The next [domestic] game is against Tottenham and Tottenham are competing with us for the same target, to be safe in the Premier League. I must try to compete in both competitions, [but] I cannot forget the next game in the Premier League.
“I believe to play on our level and to compete in a way I want to compete we need to be fresh mentally and physically. If we were in a safe position in the Premier League table, it [would be] completely different.”
Ola Aina, Nikola Milenkovic and captain Morgan Gibbs-White are among the players that have made the trip to Denmark, though whether any feature in the Europa League decider remains to be seen.