On the back of collecting just three points from two Champions League fixtures, United are under pressure to deliver a positive result at Old Trafford.
Diallo will play no part of the game having spent much of the past two months on the sidelines, but the Ivory Coast international has called on United to be prepared for a difficult encounter against his former club.
Speaking to the club's official website, the 19-year-old said: "First of all, we must not underestimate Atalanta.
"If you underestimate Atalanta, you are making a huge mistake. They have got a great coach, a great team and they have got good fans. They press high, they don't let you play and they put you in difficulty."
Atalanta currently sit at the top of Group F, the Italian side the only club of the quartet to remain undefeated.