New boss Mourinho has begun a recruitment drive that has brought defender Eric Bailly, striker Zlatan Ibrahimovic midfielder Henrikh Mkhitaryan and the famous player Paul Pogba to Old Trafford.
"We're in a very good spot now, we think we can challenge for the Premier League," said 30-year-old Rooney.
"I think the players feel this is more like the old Manchester United."
Rooney also praised the "great work ethic" of Ibrahimovic and said United would be making a "big statement" if they managed to capture Juventus midfielder Paul Pogba.
Rooney admits United "want to put a marker down" in that match.
"I know it's a one-off game, but we want to show we can win a trophy early on," he said. "We feel that's an important event for us."
"No, I wouldn't have rested six players... it's more than half the team," said Rooney. "It was a gamble and it didn't pay off."
