Bruno Fernandes has provided Manchester United with a big boost but "one or two pieces" are needed for Ole Gunnar Solskjaer's team to be where he wants it.
Having failed to reach a deal with Sporting CP in the close season, United finally snapped up Fernandes in January in a transfer that could cost up to £67.6million (€80m).
The Portugal international has scored two goals and set up another pair in his five appearances since arriving at Old Trafford.
Solskjaer has no doubt Fernandes has provided United with something it was lacking, but he feels further additions are needed to get his team up to the standard he expects.
"We knew when we made the decisions we made in the summer it was going to take time and Rome, as I've said a few times, wasn't built in a day," said Solskjaer ahead of Sunday's trip to Everton.
"But the culture, the attitude, the fitness, the camaraderie, the team spirit, maybe even the understanding between players, have improved.
"We have missed that box-opener that Bruno is proving to be now. There was one or two pieces missing and we still know we're missing one or two pieces to be where we want to be. But it's a work in progress.
"Kieran [McKenna], Michael [Carrick] fantastic on the training ground I have to say, the coaching, and the boys are willing to learn. And now we've got more and more fit players as well."
Solskjaer has been impressed by the attitude displayed by Fernandes, who was on target from the penalty spot in a 5-0 win over Club Brugge on Thursday that sent United into the last 16 of the Europa League.
"When I send him in or when I take him off – obviously he didn't want to come off [against Brugge], that's one thing. He just loves football, he's got so much enthusiasm and has a smile about him, he wants to be out there and wants to be better," said the manager.
"I tried to send him in because it was cold and [he said,] 'Oh, no, no. I want to watch.' He just loves football, he'll probably know everything about football and is just one of these old-school boys that football is everything for him. He's been a big, big boost for us."
United heads back to Merseyside on Sunday seeking to extend a seven-game unbeaten run in all competitions and Solskjaer wants to lay the ghosts of its last visit to rest.
"That was the lowest I've been, I think you all know that and remember that. That was just a capitulation," he said, having overseen a 5-0 Europa League defeat of Club Brugge on Thursday.
"We had absolutely nothing about us, even though all the goals were more or less counter-attacks from set-plays or long throw-ins; everything you didn't want to see you saw in that game.
"Everton at home are hard to play against, with the two up front, they put the players in the box, so we knew what we were up against. I'm 100 per cent sure we'll put a better performance up."