It's possession play against gegenpressing; both systems have obvious strengths and clear weaknesses, and this week's Champions League quarterfinal second leg will be largely defined by the latter. It's a test of both managers' ability to address the alleged major shortcoming in their respective coaching philosophies. Can Klopp's side defend when under sustained spells of pressure? Can Guardiola's side guard against counterattacks?

The task for Klopp is simple: his side must prevent conceding three goals. Yes, a single away goal would be extremely useful, therefore compelling Manchester City to score at least five times. But, either way, should Liverpool be eliminated, it will be because of a defensive catastrophe.

Liverpool's defensive failures under Klopp have, in truth, been somewhat exaggerated. Thirty-five goals against in 33 Premier League games this season isn't a disastrous record. Besides, Liverpool are so effective going forward precisely because of their style of play without possession, moving forward quickly to close down opponents, often leaving their defence slightly exposed. It's a risk Klopp believes is worth taking.

Liverpool largely defend well in that respect. They do not, however, defend well in the traditional respect: at set pieces, and when their defenders are faced with obvious one-versus-one battles against dangerous, quick opponents. There have, however, been signs of improvement in recent months.

The obvious catalyst has been the January capture of Virgil van Dijk, who has adapted well to Klopp's system. Van Dijk's most notable attribute is his height, which combined with his positional sense ensures he's excellent at defending crosses. But the Dutchman is also capable of playing in a high line, which remains more important for playing in a Klopp side. Alongside him, Dejan Lovren has looked more composed.

Arguably more important, though, has been the rise of two previously unheralded full-backs. Andy Robertson has proved an excellent signing, snapped up from relegated Hull City with a reputation as a dependable, steady performer. Even at the time it appeared an astute purchase, but Robertson has surpassed everyone's expectations, perhaps including his own, and proved Liverpool's best defensive performer this season. His shackling of Raheem Sterling in the 4-3 victory over Man City in January was particularly impressive, and probably contributed to Guardiola's decision not to play Sterling last week, instead playing a peculiar attacking system that robbed City of width and meant they didn't record a single shot on target.

Last week, meanwhile, Robertson was overshadowed by the man-of-the-match performance from Trent Alexander-Arnold on the opposite flank. Alexander-Arnold hasn't been as consistent as Robertson, and has often rotated with the injured Joe Gomez anyway. The previous game, at Crystal Palace, he was Liverpool's weak link and was therefore targeted by Guardiola at Anfield, with Leroy Sane deployed on his flank and City's midfielders switching the ball that way frequently. It was a logical approach, yet Alexander-Arnold stood firm, reading the game and matching Sane's speed. He might still be targeted again, but last week felt like a coming-of-age performance.

Suddenly, Liverpool's defence looks secure. Yes, defending remains about collective rather than individual play, but Liverpool's previous defensive mistakes were so often about needless individual errors that weren't really Klopp's fault. His faith in his new full-backs, and his determination to go for Van Dijk -- and Van Dijk alone, even when that avenue was shut down last summer -- appears to have paid off.

That's the main storyline: whether Liverpool can hold strong, shut out City and progress. But for Guardiola's coaching reputation, the here isn't really about progressing or not progressing. There's a more serious danger to his coaching reputation than the prospect of City not scoring. What if City go all-out attack, get caught on the counterattack, lose 3-0 and end up going down 6-0 on aggregate? City have conceded seven goals in their past two games against Liverpool, and a repeat isn't impossible.

For all the questions about Guardiola's defensive record (it's generally very good) and his lack of a Plan B (it's not usually required), there's a more serious issue about how susceptible his Barcelona and Bayern Munich sides were to counterattacking football. His two "failures" to win the Champions League with Barca came when they faced Inter and Chelsea sides who sat back and broke quickly. His Bayern spell is best remembered, in Champions League terms, for them being destroyed on the break by Real Madrid, losing 5-0 on aggregate.

In a sense, the same thing happened in the first leg -- although Guardiola's system wasn't really to blame. The opener, scored by Mohamed Salah, came after a City corner rather than resulting from their formation or approach in open play. City were largely cautious with the positioning of their midfielders, and in open play were disappointing going forward rather than hopelessly exposed at the back.

In truth, guarding against the counterattack has arguably been the area where Guardiola has evolved most since his Barcelona days. His use of "inverted full-backs" at Bayern was about packing the centre of the pitch and preventing the opposition from breaking quickly through the middle. City's system this season has been more complex than often considered, with Kyle Walker becoming an extra central defender and Fabian Delph moving inside from left-back to play in the midfield line, forming a "2-3" or "3-2" block that allows City to effectively play with a front five.

It remains to be seen whether City can play that way, however, in a game in which they must score at least three times. Guardiola may ask his full-backs to overlap, exposing Fernandinho and the centre-backs against Liverpool's devastatingly quick front three. It would be a risk, but a risk City will probably need to take at some point.

Another convincing Liverpool win would, however, prompt further questions about Guardiola's ability to tactically manage two-legged Champions League ties against sides playing on the break. Here, Guardiola is not solely seeking to keep Manchester City in the tie, but also seeking to defend his coaching philosophy.