CLEAN : Chelsea to face Basel in Europa League

The transcript discusses the challenges Benfica faces in the Champions League, highlighting the difficulty of competing against teams like Fenerbache and Basil. Fenerbache is described as an unknown quantity, while Basil is noted for their strong performance against Premier League teams, including a significant impact on Manchester United's qualification in a previous season.

What unknown factors were mentioned regarding the competition?

Why should the team not underestimate Basel according to the text?