London - Jose Mourinho hopes Diego Costa's return from suspension will provide troubled champions Chelsea with the spark to ignite their spluttering campaign.
Feted as kings of the Premier League in May, just five months later the Blues are languishing in 16th place following a 3-1 home defeat against Southampton.
That loss came amid reports of a dressing room mutiny against the Chelsea boss.
And, despite public backing from Chelsea owner Roman Abramovich, Mourinho cut an agitated figure this week when he launched a scathing attack on the Football Association after he was fined and given a suspended one-match stadium ban following his criticism of the officials in the Southampton match.
With tensions running high at Stamford Bridge, Mourinho is relieved to welcome back Costa after a three-match ban and said the Spain striker's return had lifted morale ahead of Aston Villa's visit on Saturday.
"On Friday we had a good conversation. We laughed a lot because Diego Costa found the reasons for the bad results," Mourinho said.
"I cannot tell you but he gave us the solution to go back to victories.
"We cannot run away from the reality of the table in the Premier League.
"The numbers are very cruel and we need points, but obviously we know we're not going to be relegated."
Meanwhile, Jurgen Klopp has challenged Liverpool's under-performing stars to rediscover their swagger when the new Reds boss gets his first taste of the Premier League against Tottenham.
All eyes will be on Klopp's eagerly anticipated debut at White Hart Lane following the highly-regarded German's recent appointment as successor to the sacked Brendan Rodgers.
The charismatic 48-year-old's impressive track record at Borussia Dortmund has established him as one of Europe's top coaches and his arrival has rekindled enthusiasm among Liverpool fans who had grown disillusioned with Rodgers' trophyless reign.
But, with Liverpool slumping to 10th place after just one win in their last nine matches in all competitions, Klopp is well aware he faces a major rebuilding job before he can dream of emulating legendary Anfield managers like Bill Shankly, Bob Paisley and Kenny Dalglish.
"I have met two kinds of people in the last week: most of them say 'We'll win the league' and the other guys look at me like 'What have you done? Why are you here?'," Klopp said.
"Both are not right in this moment. It is not interesting what people think about this."
While Klopp is cautious about revealing his own ambitions, he has already identified one key problem that needs to be solved if Liverpool are to get back on track quickly.
He believes the players were hamstrung by a fear of failure as the pressure mounted on Rodgers and he wants them to forget about past mistakes.
"Some things you can change instantly: mentality, readiness," Klopp said.
"I want to see more bravery, more fun in their eyes. I want to see that they like what they do."
While Klopp will steal most of the headlines this weekend, new Sunderland manager Sam Allardyce returns to the Premier League facing arguably the toughest challenge of his career.
The second bottom Black Cats turned to Allardyce after Dick Advocaat quit, making him the first man to take charge of bitter north-east rivals Newcastle and Sunderland.
Allardyce, who left West Ham at the end of last season, has a well-earned reputation for helping clubs punch above their weight.
But Sunderland have failed to win any of their first eight matches and defeat in Allardyce's debut at struggling West Bromwich Albion would be a hammer blow.
"It's a big challenge. Even at this early stage of the season, it's clear that we are in trouble," Allardyce said.
"It could take the vast majority of our 30 matches to get safe."
Leaders Manchester City host Bournemouth bolstered by captain Vincent Kompany's return after a five-game injury absence, but Manuel Pellegrini's side will be without star striker Sergio Aguero and key midfielder David Silva after both suffered knocks on international duty.
Second placed Arsenal will face Watford for the first time in nine years when they travel to Vicarage Road, while third placed Manchester United are at Everton.
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