LONDON: After the Champions League knockout phase was opened by teams with a combined 24 European titles, the spotlight shifts to those with far less of a continental pedigree.

Just one of this week's four Round of 16 matches features former European champions, with FC Porto and Juventus both two-time winners meeting in Portugal on Wednesday.

Atletico Madrid, which has the undesired record of being a three-time losing finalist, plays its first leg away at Bayer Leverkusen the previous night. A return to European action should provide some respite from domestic struggles for Leverkusen, which is mid-table in Germany.

Leicester's plight at home in England is far more perilous. The ailing Premier League champions are only one point above the relegation zone as they resume their first Champions League campaign with a trip to Sevilla, which is flying high in third place in Spain.

There's a first-leg meeting between the Premier League's second-place team and France's top team on Tuesday when Manchester City hosts Monaco. Although City has been one of world soccer's biggest spenders over the last decade, it has yet to progress beyond the semifinals in the Champions League as it seeks European silverware to firmly establish itself in the elite.

Here's a closer look at the games:

PORTO vs. JUVENTUS

The Serie A standings suggest all is smooth for Juventus, with its seven-point lead. But below the surface, there are cracks in the camp. Defender Leonardo Bonucci became embroiled in a heated argument over substitutions with coach Massimiliano Allegri after a 4-1 win over Palermo on Friday.

It was the third time in three weeks that players had questioned Allegri's decisions. Paulo Dybala and Stephan Liechtsteiner also openly displayed their displeasure.

"There has always got to be respect and there's a way to say things that's part of being polite," Allegri said. "But when there are moments of tension, there's always a chance that someone will make a mistake."

Porto certainly hasn't been making many. Nuno Espirito Santo's team has won six Portuguese league matches in a row to cut Benfica's lead to one point, fueled by January signing Tiquinho's four goals

BAYER LEVERKUSEN vs. ATLETICO MADRID

Leverkusen's inconsistent season the team is 20 points behind Bayern Munich after 21 Bundesliga games has led to persistent speculation on the future of coach Roger Schmidt, now in his third season at the club.

Two victories have eased the pressure on Schmidt somewhat, while the emergence of 17-year-old Kai Havertz has also provided a welcome distraction.

Leverkusen's youngest ever player in the Bundesliga, Havertz provided three assists in the last two games and displayed technical ability and maturity.

Regardless of Havertz's presence, Leverkusen striker Stefan Kiessling sees Atletico, which lost to Real Madrid in last season's final, as the favorite on Tuesday.

"Atletico has strengthened further since our duel two years ago," Kiessling said, referring to the 2015 shootout loss in the same Round of 16.

SEVILLA vs. LEICESTER

It's been a miserable two months since Leicester was last in Champions League action. The team that captivated the sporting world by winning the Premier League last season after starting out as 5,000-1 outsiders is sliding toward relegation.

To make matters worse for manager Claudio Ranieri, Leicester was humiliated in the FA Cup by third-tier Millwall on Saturday.

Sevilla, by contrast, is on a high in Jorge Sampaoli's first season in charge. The team is on course to match its third-place finish in 2009 but is only three points behind leader Real Madrid, which does have two games in hand.

Sevilla striker Stevan Jovetic will be a familiar face to some Leicester players, having spent two years at Manchester City between 2013 and 2015. But the Montenegrin is unrecognizable from the striker who managed only 11 goals in 44 appearances in England.

Since signing on loan from Inter Milan last month, Jovetic has netted three goals for Sevilla, including two in two games against Real Madrid. He also set up both goals in a 2-0 victory over Eibar on Saturday.

MANCHESTER CITY vs. MONACO

City's top priority will be to keep attacking midfielder Bernardo Silva quiet. Diminutive in stature, but extremely quick, the skillful Silva also has an eye for goal, a lethally accurate shot from outside the penalty area and makes great runs into the box to score with his head.

Silva has already scored against Premier League opposition this season, when Monaco 2-1 won against Tottenham during the group stage at Wembley Stadium.

"He's our little phenomenon," Monaco fullback Djibril Sidibe said. "He can dribble past two or three players and he's unpredictable."

City, in Pep Guardiola's first season in charge, is equally unpredictable. Having established a four-point lead early in the season, it is now eight points behind leader Chelsea.

City also experienced a setback in the FA Cup on Saturday, when it was held by second-tier Huddersfield, although Guardiola made eight changes for the game as he rested players.

Guardiola has won all seven previous Round of 16 matches in charge of Barcelona and Bayern Munich.