Ruben Amorim branded his team as the worst “maybe in the history of Manchester United” after a 3-1 defeat against Brighton on Sunday led to the team being booed off the pitch at Old Trafford.

The defeat leaves United in 13th with 26 points, 10 points above the relegation zone, on a day when fans and former players paid tribute to the late Denis Law. It was United’s sixth home league defeat of the season, the most from their opening 12 home matches of a league campaign since 1893-94, 131 years ago.

Amorim pointed to his record since replacing Erik ten Hag in the autumn. “In 10 games in the Premier League, we won two. I know that. We are the worst team maybe in the history of Manchester United,” he said. “I know you want headlines but I am saying that because we have to acknowledge that and to change that. Here you go: your headlines.

Related: Brighton’s brilliance and André Onana’s blunder rock sorry Manchester United

“Imagine what this is for a fan of Manchester United, imagine what this is for me. We are getting a new coach who is losing more than the last coach. I have full knowledge of that. I am not going to change [his 3-4-3 system], no matter what. I know we can succeed but we need to survive this moment. I am not naive. We need to survive now.”

Amorim stated everyone at United is to blame. “It’s hard to explain, we have to acknowledge the moment and not go around the problem,” the head coach said. “Everybody here is underperforming, no matter what the circumstances, we are underperforming and have to accept that.”

This was a seventh defeat in Amorim’s 15 matches in charge. “It’s unacceptable to lose so many games. For any Premier League club – [but] imagine Manchester United. So it’s a really hard moment but we have to continue, we have to continue, there is no other way. We need to suffer and continue.”

Amorim was asked how hard it can be for elite footballers to adjust to his system. “They are used to different things,” the Portuguese said. “Then sometimes you have one team that almost wins the league and then the next season is really bad without confidence. Our players are really nervous. If I feel it the players feel it a lot. The only way is to continue to win games.”

Marcus Rashford was again not in the matchday 20. Amorim has previously stated the forward was left out for “training reasons”. He was asked if he felt let down that a player who could help the side is unavailable.

“No. It is his choice,” he said. “I don’t want to focus on this bad moment [and say]: ‘In this game we lost [because] Rashford is not here.’ Rashford is out of this moment. I am not going to put a player I don’t believe is the best for the team.”

Goals by Yankuba Minteh, Kaoru Mitoma and Georginio Rutter for Brighton were answered only by Bruno Fernandes.