Manchester City's bid to regain the Premier League title faces a defining moment against leaders Liverpool this weekend, while Ole Gunnar Solskjaer fights to silence the critics as troubled Manchester United take on Everton.
City are already five points behind Liverpool, albeit with a game in hand, and cannot afford to lose to the champions at the Etihad Stadium on Sunday.
Pep Guardiola's side have allowed Liverpool to steal a march on them after winning just three of their first six league games.
Although City have won five of their last six games in all competitions, including a midweek Champions League success against Olympiakos, they remain some way short of their peak form.
Hampered by Sergio Aguero's recurring injury problems, City have lacked a cutting edge at times.
Guardiola can take heart from the return to fitness of Brazilian striker Gabriel Jesus, who came off the bench to score against Olympiakos.
Acknowledging the significance of the Liverpool match to City's title hopes, Jesus said: "It's a very important game for us. It's a direct confrontation against the leader of the table.
"We need to be very focused, especially playing at home. We need to play our way and try to win the game. We need to win those three points if we want to aspire to win the Premier League again."
While City have made a spluttering start, Liverpool appear back to their best despite the absence of key defender Virgil van Dijk.
Klopp has been forced to alternate between inexperienced youngsters Rhys Williams and Nat Phillips as Joe Gomez's partner in central defence, but the Liverpool machine is still running smoothly.
Jurgen Klopp's team have won five games in all competitions and conceded just two goals since Van Dijk suffered the serious knee injury that is likely to rule him out for the rest of the season.
Liverpool, one point clear of second placed Leicester, crushed Atalanta 5-0 in the Champions League in midweek thanks to in-form Diogo Jota's hat-trick.
"We are not a team of only one player. The last weeks have been difficult times because we have lost some important players in our team, but now we have many coming back as well," Liverpool keeper Alisson Becker said.
- Under pressure -
Meanwhile, Manchester United's dismal start to the season has left Solskjaer in danger of the sack.
After two successive losses, another damaging defeat at Everton would put the Norwegian under intense pressure amid reports United's board have made contact with representatives of former Tottenham manager Mauricio Pochettino.
United's shock 2-1 defeat at Istanbul Basaksehir in the Champions League on Wednesday was an especially embarrassing night for Solskjaer as his team's defensive frailties came back to haunt him yet again.
Beaten by Arsenal in the league last weekend, United are off to their worst start at home since 1972, so Solskjaer might welcome an away game against an Everton side who have lost their last two games.
But Solskjaer, whose side sit just four points above the relegation zone, will know the forthcoming international break potentially presents an opportunity for his dismissal if he doesn't inspire a win against Everton.
United, losers in three of their six league games, have not been beaten in four of their first seven in a league campaign since 1989-90.
"I decline to comment on such a thing. Of course, it's early on and opinions are out there all the time. You've got to stay strong," Solskjaer said after the shambles in Istanbul.
"I'm employed by the club to do a job and I do that to the best of my ability with my staff."
Elsewhere this weekend, if Liverpool drop points against City, then Leicester, who host Wolves, or Tottenham, who travel to West Bromwich Albion, could seize first place.
Fixtures (all times GMT):
Brighton v Burnley (1730), Southampton v Newcastle (2000)
Everton v Manchester United (1230), Crystal Palace v Leeds (1500), Chelsea v Sheffield United (1730), West Ham v Fulham (2000)
West Brom v Tottenham (1200), Leicester v Wolves (1400), Manchester City v Liverpool (1630), Arsenal v Aston Villa (1915)