Don't forget that there is no difference between the performance of Lille and that of Dortmund this season in their domestic league as a matter of fact both teams have achieved better results in the champions League than their league so I don't think Dortmund will have an easy match against Lille if they try to underestimate them they may end up losing the game and Lille advancing to the round of 8. Dortmund is doing well in the champions League which is the only thing I can say and winning the champions league this season should be their target since they couldn't do it when they met Real Madrid in the finals, if they are able to show good performance I think they will have the advantage of defeating Lille.
You are right. Both Lille and Dortmund are performing irregularly in their domestic leagues. Lille is in fifth place in the Ligue 1 points table. Lille lost to PSG by a big margin a few days ago. On the other hand, Dortmund is in tenth place in the Bundesliga points table.
However, Lille played very well in the first round of the Champions League. They defeated a big team like Barcelona. They qualified for the Champions League round of 16 from seventh place in the table. So Lille cannot be considered a weak opponent for Dortmund. Although Dortmund is a renowned team, they have the possibility of losing against Lille.
It was a bad match for Lille against PSG last weekend. They are going into the Champions League match with a negative situation, but their opponent Borussia Dortmund is far from their old days in the Bundesliga. If it was last year's Borussia Dortmund, I would say they would easily pass this round, but the current situation is far from certain. We all saw that Atalanta was the favorite but was eliminated by losing in both matches. So it would be very wrong to talk about a match with certainty. Both teams are very strong and both teams will have a good fight.