The Reds travel to Italy this week for Wednesday’s Champions League away tie at Juventus - a game they dare not lose. Four days later they travel to the Etihad to face Pep Guardiola’s title holders.
United have conceded first in four of their last five games but defender Smalling has no fears about facing in-form Ronaldo or City.
He said: “We know we're going into a very tough week now but we can come out with some good results and it can be seen as a good month, considering it was probably one of our toughest months, especially a tough month now and potentially after the international break.
“We need to take the second half performance that we had against them at home and we need to do that from the off and we'll give them a good game and get chances.”
Juventus outclassed United at Old Trafford two weeks ago and have won all but won of their 14 games in all competitions this season, drawing the other.
Their defensive instability contrasts sharply with this stage last season when they had posted eight clean sheets and had shipped just five goals.
Smalling admits his seventh-placed side are under huge pressure to close the gap on the Premier League leaders. Defeat at Juventus could see them slip to third in their Champions League group behind Valencia.