Jonny Evans told ITV's Gabriel Clarke that Manchester United need to cut out the little mistakes after they defeated Braga 3-2.
The Northern Irish defender scored United's second as they came from two goals down to win against the Portuguese side.
"It's poor from us as a team, to let teams get crosses in. Simple things like not talking to each other will cost us against bigger teams," Evans explained.
Despite the poor start to the game, United created a host of chances, as they made it nine points from their opening three games.
"At Old Trafford we always feel like we can score goals, we have great attacking player. Some of the link-up play was excellent."
Javier Hernandez was praised by Evans after netting twice for United to salvage the game.
"He took his two goals well, he's good in the air, the timings of his leaps, and his second goal was superb.