Bundesliga and La Liga: Will Bayern Munich and Real Madrid be upset by the underdogs?
In the Bundesliga, Bayer Leverkusen are top of the table and host Bayern Munich (17:30 GMT), who are second and two points behind Xabi Alonso's side.
In La Liga, Girona travel to Real Madrid (17:30 GMT) knowing a victory would take them above Carlo Ancelotti's side and into first place.
BBC Sport takes a close look at the two fixtures that may prove hugely significant in who ultimately wins the league titles.
Leverkusen threatening to thwart Kane's trophy hopes
When Harry Kane moved from Tottenham to Bayern in August, it seemed like the end of his long wait for a trophy was a foregone conclusion.
The German giants have won the Bundesliga every season since missing out in 2011-12, but in Kane's first campaign their hopes of continuing that run are coming under real threat from Leverkusen.
Alonso's side are top with an incredible 52 points from a possible 60, form that has seen their head coach linked with Liverpool.
Bayern are just behind on 50 and this is the first time in Bundesliga history that two teams have collected 50 points after 20 matches.
As top-of-the-table games go, it doesn't get much bigger, with Bayern having to travel to the BayArena knowing a victory would put them top of the table, but defeat would leave them five adrift.
Bayern were pushed all the way last season as well, with Borussia Dortmund only missing out on the title on the final day of the season.
German football journalist Raphael Honigstein said on the BBC Football Daily Euro Leagues podcast: "What is different this year compared to recent years - where Bayern have looked vulnerable and other teams look like they might make it - it was because Bayern were having a poor season, but this year Bayern are having a great season.
"They have 50 points, Leverkusen have 52 from 60. It is unbelievable consistency.
"It is not a case of Bayern being weak and another team being good. Bayern are decent and another team is playing on a level that seems almost unsustainable."
The big factor in Bayern Munich's favour is Kane.
The England captain has had a brilliant first season in Germany and is the league's top scorer with 24 goals.
Despite that impressive record, Kane is determined to be even better in the second half of the campaign.
He told BBC Sport: "We have a big game coming up this week of course against Leverkusen and we have plenty more important matches to go this year, so I'm hoping I can even improve from the first half of the season, I always try and get better.
"I'm at Bayern Munich who have won the league for the last 11 years so there's an expectation to win that league this year.
"Of course Leverkusen have started amazingly well and still undefeated so it's a really important game this weekend which I'm excited for."
Leverkusen head into the game on the back of a 30-game unbeaten run in all competitions, while Bayern have won 12 of their last 14 Bundesliga games, losing two games during that run.
"I think Bayern will come good because they can still play better and they have Harry Kane and I think that combination will prove too much," Honigstein added.
"But of course if Leverkusen use their momentum and beat Bayern on Saturday then all the drama and stories that will come out of Munich after that game, then they have a chance."
Will Real Madrid end Girona's dream?
La Liga is often a tussle between Real Madrid and Barcelona, but this season Girona have muscled into the mix.
Despite only playing in their fourth top-flight campaign, Girona have upset the traditional order and have showed no signs of falling away.
They have lost just one game out of 23 in La Liga, with their all-out attack approach paying dividends. They have scored 52 goals this season - more than any other side in the league.
Their one defeat, however, did come against Real Madrid, underlining the size of the task that awaits them when they travel to the capital.
"It is amazing what has happened," Spanish football expert Guillem Balague said on the BBC Football Daily Euro Leagues podcast.
"Real are favourites on Saturday and a victory for them could kill the league.
"But for Girona the target is really the Champions League. So whatever happens to Girona it will never be considered a failure, even if they don't win the league.
"Have they got a chance? Of course they have a chance. They have some key players missing but it is an unexpected story and one we are having a lot of fun with."
Real Madrid, of course, have England midfielder Jude Bellingham in their ranks, but they go into this game with a defensive headache - not ideal against La Liga's top scorers.
Nacho is likely to miss out with a muscle issue while Antonio Rudiger has a knee injury. David Alaba and Eder Militao are also still sidelined.
Despite that, Real boss Ancelotti is unconcerned and sees Saturday's game as a chance to lay down a significant marker in the title race.
"We are leaders and we have another chance to make a statement win," Ancelotti said.
