Romelu Lukaku has assured Manchester United fans that the club will sign "a lot of good players" in the summer after what has been a difficult week for the Premier League giants.

United were knocked out of the Champions League midweek by an unfancied Sevilla side, prompting manager Jose Mourinho to question the club's "football heritage."

Then, after Saturday's 2-0 FA Cup quarterfinal win over Brighton, the United boss was once again on the front foot -- this time outlining a "lack of class, lack of personality, [and] lack of desire" in his squad.

Lukaku, however, is unconcerned about his team's future. The striker was eager to stress that one good transfer window could help bridge the gap to United's crosstown rivals -- and Premier League champions-in-waiting -- Man City.

"We are Manchester United, we have to improve every year and I know that a lot of players, a lot of good players, will come in next season. That's for sure," said Lukaku after Saturday's win.

"That is something I look forward to, in order to improve the squad, and what the manager also looks forward to because next year we have to win.

Romelu Lukaku scored Manchester United's opener in their 2-0 win over Brighton on Saturday. Getty

"We will have to try and win as many trophies as we can.

"I don't believe we are really that short in being able to compete in the big ­competitions.

"We knew immediately after the game against Seville that we weren't good enough, so we accept the criticism."

One player who is yet to make an impact for United is January signing Alexis Sanchez. The Chile international arrived amid great fanfare from Arsenal, but has registered just a single goal in his first 10 appearances for the club.

"As long as he keeps working hard like he does, I think he'll come good for us," Lukauk added. "He is a quality player with a lot of assets.

"Look at my situation. I started really well and then had the dry spell in November and December. But at the end of the day with hard work you are always going to get through it."