You don't need to underestimate Lyon because they might pull some stunts on that day. Don't forget that they are in form. On the other hand, United shouldn't find it difficult to win Lyon and qualify to the semifinals because they are performing pretty good in this league. United is unbeaten and I don't think that they will mess up the only chance to put things right in order to be in UCL next season.
Every match must always be taken seriously by any team so that no one should be underestimated because Lyon themselves are also quite aware that they will face a team that has never lost in the Europa League this season so Lyon will also use all their abilities to give Manchester United a very tough fight. But on the other hand I am also more confident in Manchester United because the team is certainly very ready for all the pressure from any opponent in the Europa League this season including the match with Lyon in the quarter-finals later.