Manchester City and Arsenal have led the way in the last two Premier League title races but both teams have hit a slump heading into the weekend when their squad depth will be put to the test as they aim to reel in leaders Liverpool.
Mikel Arteta's Arsenal have looked flat in recent outings and two straight 1-0 losses away at Newcastle United and Inter Milan have left the club fifth in the Premier League and 12th in the Champions League respectively.
Although they will be glad to see their influential skipper Martin Odegaard finally back in the fray after being injured in August, questions remain about whether he can start or even play 90 minutes in Sunday's London derby at Chelsea.
Without Odegaard, Arsenal have struggled to create chances through the middle while the Norwegian's eye for goal has also been sorely missed by an attack that has looked sterile in recent matches.
With Leandro Trossard, Gabriel Martinelli and Gabriel Jesus misfiring, the burden to provide the magic touch has fallen on 23-year-old Bukayo Saka but he cannot do it all alone.
Arsenal have lost three of their last six games in all competitions - as many defeats as in their previous 32 matches.
Injuries to Declan Rice and Kai Havertz are also concerns while Arteta did not rotate his squad, playing near-identical line-ups in both games which see tired legs at Stamford Bridge where Raheem Sterling cannot play against his parent club.
On the other hand, Chelsea, also on 18 points but fourth with a marginally better goal difference, are likely to rotate on Thursday in their Conference League game against Noah, with playmaker Cole Palmer resting as he is not in their squad.
Arteta has attempted to energise his players in the wake of Wednesday's controversial loss at the San Siro.
"The performance, the attitude, the dominance that we showed against one of the best teams in Europe in this stadium - I haven't seen it in all the other games that I've watched," he said.
"If we play the way we played, we'll have a big chance to win against Chelsea.
INJURY COST
Champions Manchester City, who face a trip to Brighton & Hove Albion, have been counting the cost of injuries and, after some heavy rotation, Pep Guardiola's side have lost their last three games in three different competitions.
Tuesday's 4-1 mauling at Sporting in the Champions League will sting, all the more so because the Portuguese side's manager Ruben Amorim is moving to City's rivals Manchester United later this month.
Apart from City's Ballon d'Or winner Rodri, key players such as Jack Grealish and John Stones remain sidelined but Guardiola is relishing the challenge of overcoming adversity and navigating his team through a rough patch.
"It's a tough challenge, but I'm here. It will be a tough season - we knew that from the start," he said. "But this is what it's. I like it, I love it, I want to face it and lift my players and try it."
City face a tricky task at eighth-placed Brighton where Fabian Huerzeler is developing a side which has had 10 different scorers this season, though they have let several leads slip.
Arne Slot's high-flying Liverpool lead City by two points but may find themselves in second place in the late game on Saturday when they host Aston Villa, who are experiencing a City-like slump of their own having lost three in a row.
For Liverpool, losing keeper Alisson to injury last month was seen as a huge setback but Slot's side have passed the test with flying colours in an unbeaten run with five wins in their last six games as Mohamed Salah and Luis Diaz lead the charge.
Interim Manchester United boss Ruud van Nistelrooy's last match in charge is at home to Leicester City on Sunday when this season's surprise package third-placed side Nottingham Forest host mid-table Newcastle United.
Bottom side Wolverhampton Wanderers are still seeking their first win and host fellow strugglers Southampton while Ipswich Town, the only other side without a victory in the top flight, are at in-form Tottenham Hotspur, who are seventh.