The Champions League and Europa League group stages get under way this week.

After last season's alterations to both competitions as a result of the coronavirus pandemic, which continues to affect the game across the globe, what format will the 2020-21 tournaments take, when will the games be played and will fans be allowed in to see them?

BBC Sport answers all your questions in our preview guide...
What are the formats for the tournaments this year?

Uefa's solution to last season's Champions League competition being disrupted was to stage a "final eight" knockout tournament played across 12 days in Lisbon, German side Bayern Munich emerging as winners.

A similar format was used for the remaining Europa League ties, which were staged in Germany with the competition won by Spanish side Sevilla.

This season sees a return to the more familiar format for both tournaments.

In the Champions League, 32 teams from 14 countries have already been drawn into eight groups of four and will play each other twice (home and away), with the top two from each group qualifying for the knockout rounds. The eight third-place teams drop into the Europa League at the last-32 stage.

The Europa League has 12 groups of four, with home and away games to decide who qualifies for the knockout rounds courtesy of a top-two finish.

The last-32 stage to semi-final of each tournament will consist of home and away legs.

When are the rounds played?

With delays to the 2019-20 season meaning the Champions League and Europa League finals were not played until late in August, fixtures for the 2020-21 competitions were delayed.

The Champions League group stage gets under way on Tuesday, with Europa League group-stage fixtures commencing on Thursday.

Here is a breakdown of the fixtures and when they take place...
Champions League and Europa League fixtures
Champions League Europa League
Group matchday 1 20/10/2020-21/10/2020 Group matchday 1 22/10/2020
Group matchday 2 27/10/2020-28/10/2020 Group matchday 2 29/10/2020
Group matchday 3 03/11/2020-04/11/2020 Group matchday 3 05/11/2020
Group matchday 4 24/11/2020-25/11/2020 Group matchday 4 26/11/2020
Group matchday 5 01/12/2020-02/12/2020 Group matchday 5 03/12/2020
Group matchday 6 08/12/2020-09/12/2020 Group matchday 6 10/12/2020
Last 16 16/02/2021-17/03/2021 Last 32 18/02/2021-25/02/2021
Quarter-finals 06/04/2021-14/04/2021 Last 16 11/03/2021-18/03/2021
Semi-finals 27/04/2021-05/05/2021 Quarter-finals 08/04/2021-15/04/2021
Final 29/05/2021 Semi-finals 29/04/2021-06/05/2021
Final 26/05/2021
When do matches kick off?

Group-stage fixtures in both competitions will kick-off at either 17:55 BST/GMT or 20:00.

You can see the full list in our fixtures pages for the Champions League and Europa League.
What is the situation with fans?

When they returned after a five-month absence in 2019-20, Europe's premier club competitions were played out behind closed doors in bio-secure environments.

At the start of October, Uefa announced that fans would be allowed into stadiums for Champions League and Europa League games, but only in those areas where local law permits it.

So, as it stands, fans can attend games in France and Germany, who have started to let supporters return in restricted numbers, but not in England, where all fixtures continue to be played behind closed doors.

Where permitted, stadiums can be filled to a maximum of 30% capacity for this season's European games. Away supporters will not be allowed at games as it stands.

Uefa's decision came after a successful pilot, which saw 15,000 fans attend the European Super Cup match between Bayern Munich and Sevilla at the Puskas Arena in Budapest, Hungary.
Where are this year's finals?

This season's two final venues are the same as those originally scheduled to host the 2020 deciders.

The Champions League final will be played in the Ataturk Olympic Stadium in Istanbul.

The 70,000-capacity venue is used for Turkish national team fixtures and has, at various points, been the temporary home for Istanbul clubs Galatasaray, ?stanbul Basaksehir and Besiktas.

Famously, it hosted the 2005 Champions League final, which saw Liverpool come back from 3-0 down to draw 3-3 with AC Milan, before beating them on penalties.

The Europa League final will take place at Poland's 41,620-capacity Gdansk Stadium, home to Lechia Gdansk.
Who are the favourites to win?

Holders Bayern Munich are the frontrunners again for this season's Champions League, after they so ruthlessly tore apart the competition in 2019-20's mini-tournament.

Unsurprisingly, Manchester City and Liverpool lead the English challenge, with Chelsea and Manchester United behind Paris St-Germain, Juventus, Barcelona and Real Madrid with the odds-makers.

Teams dropping down from the Champions League to the Europa League will alter the make-up of the latter after the group stage.

But as it stands Premier League duo Arsenal and Tottenham are among the favourites for the Europa League, ahead of Italian pair AC Milan and Napoli.

Leicester are the other English side in the competition, which also contains Scottish representation with Old Firm pair Celtic and Rangers.