There's enough room for error. I don't think I'm a fan of these unnecessary pressure from fans, else players and non fans because they spent hugely. The improvements will come game after game. That game against Grimsby should have been a win only of players in that game had stepped up. All moaning and whining aside, focused entirely on the next game. It's either we burn Burnley or they burn us. 
You must admit, the last game Man United played against Grimbsy Town did absolutely nothing to restore a little bit of confidence to the fans so you wouldn't fault supporters from feeling the way they do especially after spending so much to bolster the club and better its performance.
It's still early in the new season of the premier league but it wouldn't hurt to see a better performance from the team. They've been down for so long and we're all eager to see a much better performance. We can only hope for a good performance in the game against Burnley. Good enough for a win.