Why are there Champions League games on Thursday and will it be every week?

The UEFA Champions League returns with some significant changes - including the days fixtures are played on.

Arsenal fans may have noticed that their opening European tie - a tough away trip to Italy where they'll face Europa League winners Atalanta - won't be taking place on the traditional Tuesday or Wednesday that has become a custom in the competition.

Instead, the two will face off on Thursday evening, three days before the Gunners visit the Etihad to renew their title-fighting rivalry with Pep Guardiola's Manchester City and four days after their 1-0 away win in the North London Derby.

Fans of other clubs in the newly formatted competition may wonder if they, too, will have to watch their sides play on a Thursday - a day normally allocated to the Europa and Conference League - but that is not the case.

As part of the new league format, UEFA has announced that each of their three competitions will have an exclusive matchweek during which fixtures from the other two tournaments will not be played.

This exclusive window has been named Matchweek 1 for the Champions League, meaning that only UCL fixtures will be played this week. UEFA have opted to spread the matches across three days instead of the normal two, so games will be played on Thursday.

However, this will only happen for this exclusive game week and won't occur again. Both of the other tournaments will also have an allotted week in which only games from either the Europa League or Europa Conference League will be played.

The revamp to the Champions League and other tournaments doesn't stop there. As mentioned, teams will play eight group matches, four at home and four away, but these ties will all be against different outfits.

Each team has been placed into a single league instead of the traditional eight groups, and those who finish in the top eight will automatically qualify for the round of 16.

Those who finish from ninth to 24th will face a two-legged knock-out phase. If they win, they will progress to face one of the teams in waiting. Sides who fall to 25th place or lower of the 36 will be eliminated from the respective competition outright, and there will be no pathway downward to lesser tournaments as there has been in previous years.

Mikel Arteta's Gunners are not the only English side in action when they travel to Bergamo this week. Aston Villa face a Swiss trip to take on Young Boys in an earlier 17:45 tie on Tuesday, and Liverpool travel against AC Milan later in the evening.

Manchester City also welcome the side they faced in the final two years ago, Inter Milan, on Wednesday night. All 500 of this year's Champions League fixtures will be aired via TNT Sports.