ANALYSIS

Diego Costa is regarded as one of Chelsea's most important players and remains their leading scorer this season, but stats from Opta show that his form has taken a dip since his offer from Chinese Super League club Tianjin Quanjian in January.

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The Spain international ultimately chose to decline the offer and remain at Chelsea to compete for the Premier League title and FA Cup glory, but he was offered a staggering £30 million-per-year contract, which would have almost tripled his salary and may have proved to be a distraction.

Did his head get turned by the offer? Well, he was subsequently dropped against Leicester City and contract negotiations with the club have slowed - it was also then that he suffered his longest goal drought of the season.

His recent performance against Crystal Palace was one of his worst displays of the season, missing key chances and only managing to get two of his nine attempts on target.

Meanwhile, he only had one attempt all game versus Manchester United and it was a wayward long-range shot. He also gave away the ball more than any other player in a Premier League match so far this season.

Ahead of his side's defeat to Crystal Palace he had scored three goals in three league games, but most were late on in matches with little riding on them.

He remains key ahead of Chelsea's final months of the season and they fought to keep him for a reason, although the data shows that his form has dipped since the transfer window, as Romelu Lukaku and Harry Kane have surged ahead of him in the goalscoring charts.

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His goals-per-game has dropped from 0.7 to 0.3 in the league, while he was registering 0.26 assists per game but has not now provided a killer pass since before the transfer saga. His shots-per-game is down slightly as well, while his conversion rate has gone down to 24.14% from 8.57%.

Costa is also creating fewer chances for his team-mates in recent weeks, as he is only getting 0.2 per game now, while before 14 January, when the story broke, it was 1.5 chances created per game. Although he is winning slightly more fouls since Tianjin's offer - up from 2.6 per game to 2.8.

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Despite his dip in form, it may be harsh to question his work-rate as he is actually winning more duels, both in the air and on the ground. Worryingly though, against Manchester United in the league he won only 21.7% of his duels.

He is also fouling more now, which could suggest that frustration has crept into his game since his big money offer, or that he is working hard to improve his recent form. It could also be a combination of the two.

In person, it is plain to see that Costa's form has declined, which is normal over the course of the season, but the stats show a correlation to his link to China.

Luckily for Antonio Conte and Chelsea, other players have stepped up in recent weeks, with the likes of Eden Hazard putting in all-star performances. Goals have been coming in from all over, from Gary Cahill and N'Golo Kante to Marcos Alonso and Pedro.

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Whether Chelsea keep Costa or lose him in the summer, with interest from the Chinese Super League still high, Chelsea will target signing another forward.

Lukaku, who has become the favourite to win the Premier League's golden boot, remains a Chelsea target after they tried and failed to secure him last summer. Real Madrid's Alvaro Morata is another who continues to interest Conte, as well as a host of younger players including Celtic's Moussa Dembele and Ajax's Kasper Dolberg.

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Conte has stated he is "confident" that Costa will stay, while Costa himself told ESPN Brasil that "everyone [at Chelsea] is on the same page," which suggests any problems between him and the club are on hold during the hunt for trophies.

In the meantime, Chelsea could do with the revitalisation of Costa to compete with their summer target Lukaku in the golden boot race, with the Everton striker going two ahead of Chelsea's frontman in recent weeks.

Costa's current form has gone from mediocre in recent weeks to much, much worse. Chelsea will need him to be great again soon if they are to earn the Holy Grail of a league and cup double in Conte's first season in charge of the club.