United had been unbeaten in their opening three pre-season friendlies but lost 4-0 to SC Braga last Wednesday and 1-0 to FC Augsburg on Saturday.
And while skipper Lascelles admits he would have preferred to have rounded off the warm-up fixtures with more positive results, he spoke to the club's official website on Wednesday afternoon as the players carried out 'walk up' media duties for broadcasters including Sky Sports and BT Sport.
"It would have been nice to get a couple of good results out of the games but what's important is we've got all the fitness we need for the first game of the season, and I think gradually we've improved," Lascelles told nufc.co.uk.
"I think the last game (against Augsburg), we can definitely take a lot of positives from that - okay, we didn't win but we got everything we need out of the game.
"The majority of the team got through (pre-season) injury free and everyone is really fit. Especially for me, last pre-season I didn't really get to play much because I was injured but I'll be looking to play this game and hopefully I'll be flying.
"And that goes for the rest of the team. Everybody looks sharp, we're training hard and we've all got our heads in the right place.
"We've managed to sort the off-field stuff; now that's out of the way, we don't have any reason why we can't go out and put on a good performance.
"We know where we stand. No-one's moaning, no-one's upset and now it's just about gelling together even more, working hard, getting a good energy around the club and the training ground - and doing what we do best which is working hard and playing as team."
Monday saw West Bromwich Albion forward Salomón Rondón become United's sixth signing of the summer, joining Martin Dúbravka, Kenedy, Ki Sung-yueng, Fabian Schär and Yoshinori Mutō on Tyneside.
And Lascelles said: "We finished tenth (last season) with the team that we've got now, and we've now got the likes of Martin and Kenedy for the full season rather than just half a season.
"And adding to that, Rondón's a very good signing - a very powerful player, fast, strong.
"I didn't play against West Brom away but when we played them at home, in terms of physicality, he's probably one of the toughest strikers I've played against.
"He's strong, he can run in behind, he can win headers and he works hard for the team. He's experienced in the Premier League so I think that's going to give us a massive boost and since he's been training with us he's looked really good.
"Mutō looks very energetic and works hard, and we've all played against Ki and technically he's excellent on the ball, a very tidy player, and I think he'll work really well in that midfield.
"So we've made some good signings and I think it won't take long for us to really gel together and carry on with the same team chemistry that we had last year."
