The major talking points ahead of this week's Champions League action

Klopp seeking European revenge against familiar foes

Liverpool's loss to Real Madrid last May was the second Champions League final disappointment for manager Jurgen Klopp. In 2013, his Borussia Dortmund team suffered heartache at the hands of Bundesliga rivals Bayern Munich at Wembley following a late strike from Arjen Robben. He will be keen to avenge that significant setback when the Reds meet the German champions for the first time since the 2001 UEFA Super Cup final, a game in which current Bayern boss Niko Kovac played. Klopp, who began his coaching career at Mainz, has won nine of his previous 23 meetings with the Bavarian club, losing 10 and drawing four. The 51-year-old may fancy his chances of turning the tables as Bayern are currently failing to hit previous heights under Kovac.

City fighting on four fronts

It is another big week for Manchester City as they once again chase an unprecedented quadruple under Pep Guardiola. City ultimately fell two trophies short last season after a shock FA Cup loss at Wigan was followed by European elimination by Liverpool. Wednesday's away game against Schalke comes four days before the English champions contest the Carabao Cup final with Chelsea having eased into the FA Cup quarter-finals on Saturday by beating League Two Newport. The last-16 draw was reasonably kind to Guardiola's team and midfielder Ilkay Gundogan, who returns to his home town of Gelsenkirchen, admits City are "clear favourites". The tie also holds individual significance for Leroy Sane, who began his career with the German club.

Ronaldo returns to Madrid to resume rivalry

Former Ajax, Real Madrid and AC Milan midfielder Clarence Seedorf remains the only man to win the tournament with three different clubs. Ronaldo, who lifted the trophy four times with Real after first triumphing with Manchester United in 2008, could emulate that achievement this term after joining Juventus. In order to do so he must first overcome old adversaries Atletico Madrid, starting with a return to the Spanish capital on Wednesday. The Portuguese has a history of inflicting misery on Atletico. He scored the decisive penalty against them in the shoot-out which decided the 2016 Champions League final, after also registering in the 2014 showpiece – one of 22 goals against them in all competitions.

Barca backing Valverde

Barcelona have slipped into the shadow of great rivals Real Madrid on the European stage in recent seasons. The five-time champions clearly believe current head coach Ernesto Valverde has the capability to turn the tide back in their favour, in the short-term at least. Valverde, who looks on course for back-to-back domestic titles, was backed with a one-year contract extension on Friday, keeping him at the Nou Camp until 2020. The Catalan club have previously been eliminated only twice at this stage of the competition and are expected to overcome a Lyon side failing to compete with Paris St Germain in Ligue 1. The French club, who host Tuesday's first leg, did defeat Manchester City in the group stage but their cause will not be helped by the suspension of captain and top-scorer Nabil Fekir.

Controversy never too VAR away

Video Assistant Referees (VAR) have been introduced into the competition for the knockout stages. The technology quickly sparked debate following the contentious decision to disallow an Ajax goal against Real Madrid last week. There initially appeared to be little wrong with Nicolas Tagliafico's header until Dusan Tadic – who was in front of Real's flapping goalkeeper Thibaut Courtois but did not touch the ball – was shown to be fractionally offside and adjudged to be interfering with play. VAR is very much still at the teething stage and currently seems in constant danger of becoming the main talking point in any game in which it is used.

ga('create', 'UA-72310761-1', 'auto', {'name': 'pacontentapi'});
ga('pacontentapi.set', 'referrer', location.origin);
ga('pacontentapi.set', 'dimension1', 'By Ed Elliot, Press Association Sport');
ga('pacontentapi.set', 'dimension2', 'bd68f926-1fc6-4e50-9982-174c09fc7776');
ga('pacontentapi.set', 'dimension3', 'paservice:sport,paservice:sport:football,paservice:sport:uk,paservice:sport:world');
ga('pacontentapi.set', 'dimension6', 'story');
ga('pacontentapi.set', 'dimension7', 'composite');
ga('pacontentapi.set', 'dimension8', null);
ga('pacontentapi.set', 'dimension9', 'sport:football');
ga('pacontentapi.send', 'pageview', { 'location': location.href, 'page': (location.pathname + location.search + location.hash), 'title': 'The major talking points ahead of this week\u2019s Champions League action'});