Manchester United manager Jose Mourinho has criticised his players for not showing Basel enough respect and accused them of being more interested in playing "PlayStation football".
United had opened up a two-goal lead within the hour in their Champions League opener on Tuesday night (12 September), thanks to goals from Marouane Fellaini and Romelu Lukaku either side of the break, but Mourinho was far from pleased with what followed.
"After 2-0, I think everything changed and we stopped to play, stopped to think, stopped to play seriously," he told BT Sport in his post-match interview.
"We stopped to make the right decisions on the pitch and we could put ourselves in trouble."
While United marked their return to the Champions League after a one-season hiatus with a convincing 3-0 win after Marcus Rashford added a third goal late on, Mourinho felt his players took unnecessary risks after going two goals up.
"Bad decisions, fantasy football, PlayStation football, tricks and when you stopped to play as a team and when you stopped to play seriously I don't like and you gamble a little bit," he added.
"The players probably felt that the game was under control with the 2-0 but football is football and you have to respect your opponent."
United are widely expected to top what is a relatively easy group, which includes Benfica and CSKA Moscow alongside Basel, but the Portuguese poured cold water on the suggestion his side was among the main challengers this season.
"For these teams - Real Madrid, Barcelona, Bayern Munich - the Champions League starts in February. Now is just the warm-up," he said.
"In February, when us English teams are trying to survive after the winter period, they are fresh and ready after this warm-up.
"We are in the second level. The second level is "let's qualify, let's make the points" and if we make the knockout phase let's enjoy playing against the big guys."
United return to Premier League action when they host Everton on Sunday (17 September) but they will do so without Paul Pogba, who lasted only 19 minutes against Basel before limping off with a hamstring injury.
According to the Manchester Evening News, the Frenchman left the ground on crutches. It is the second time in this calendar year that the 24-year-old has suffered a hamstring injury. Last time he picked up a similar injury was in March and was sidelined for more than three weeks.
After the game, Mourinho admitted he was unaware of the extent of the injury but stressed that he would not "cry" after Pogba's latest setback, though he added he expected Pogba to be out for a couple of weeks.
"I don't know [the extent]. I just know from experience it's a muscular injury. In my experience, muscular injuries stop you from playing for a few weeks, I think," Mourinho told United's official website.