Nemanja Vidic says the squad have been buoyed by four wins out of five during their pre-season preparations for the new campaign.
The Reds kicked off their warm-up fixtures with a 2-0 victory at Aberdeen earlier this month, before heading to South Africa to take part in the Vodacom Challenge.
A 1-1 draw with the Kaizer Chiefs in their opening match, was followed by three consecutive victories for United, including Sunday night's 2-1 win over Portsmouth in Nigeria.
"We're pleased to have won a few games and kept some clean sheets - it's never too early to pick up good form," said Vidic, who has featured in all but one of United's five games, in an interview with MUTV.
"We had some good matches in South Africa and we're happy with what we did out there. Our fitness is improving all the time.
"We still have another few weeks to train and make sure we're ready for the first game [against Newcastle]."
Vidic has developed a formidable partnership with Rio Ferdinand at the heart of United's defence over the last couple of seasons, but the Serb has found himself alongside two of the Reds' upcoming youngsters during his last two games.
Craig Cathcart started with Vidic against the Kaizer Chiefs, while Jonny Evans was given his chance in the game with Pompey.
"The young players have done very well," observes Vidic. "I played with Craig for the first time [on Saturday] and I thought he produced a good performance, as did Jonny.
"All the youngsters have been impressive. Rodrigo [Possebon] has looked good, and Tom [Cleverley] and Fraizer [Campbell] both scored [against the Kaizer Chiefs] so things have gone well.