#2 Injuries to key players
In the modern game, a team needs its best players even when facing minor opposition. Manchester United currently has somewhat of an injury crisis, as some ideal starters are out.
First team players like Paul Pogba, Luke Shaw, and Anthony Martial have all recently had injury problems, and some may not be available for this game. The loss of such key players means that Ole Gunnar Solskjaer has to work with players who may not offer the same level of artistry he requires from his starters.
#1 Defensive tactics
Astana's tactics may prove to be Manchester United's ultimate downfall on Thursday, because they may opt to concede possession and hit United with counter-attacks.
Crystal Palace came on top at Old Trafford by converting the few chances which came their way in the 1-2 win away from home. Also, Astana's defensive resolve could frustrate United similar to what Southampton did with 10 men.
With United having a youthful forward line, there are still doubts about how clinical they'll be throughout the season. Apart from the Chelsea game, the goals have not been in regular supply.
Their two Premier League draws this season are a testament to that. United led 1-0 in both the Wolverhampton and Southampton games. However, they failed to seal the game by adding to their tally, thus giving the opposition a lifeline.