Chelsea are in good flow this season and have lost just twice in all competitions. The Blues have been doing well against clubs they usually struggle to beat. All the players seem to be contributing well. Chelsea have 15 different goalscorers this season in the Premier League already.However, Thomas Tuchel has a few players in the squad who need to step up big time. The manager will be looking for more from the underperformers. He will need everyone to be at their best to win trophies this season.Here are 5 Chelsea players who have underperformed so far this season:#5 - Hakim ZiyechChelsea FC@ChelseaFCHakim Ziyech's work continues at Cobham this afternoon! 💪7:34 PM · Jul 14, 2020260342714Hakim Ziyech's work continues at Cobham this afternoon! 💪 https://t.co/YGr1gJ2bpWHakim Ziyech has been highly inconsistent since he joined Chelsea last year from Ajax. The Moroccan finds his feet in one game but then manages to do the basics wrong in the next one.The same has been going on over the last few months and Tuchel will be keen to get more out of the former Ajax star. The forward has had just one assist in the league this season despite making six appearances.In the Champions League, the story is not a lot different. Ziyech has a goal and an assist to his name from the four matches he has played for Chelsea.Reports suggest Ziyech will be looking to leave Chelsea in January as he is unhappy with his game time. However, if he is not delivering when he is on the pitch, it will be hard to blame Tuchel if the Moroccan forces a move away.#4 - Romelu LukakuChelsea FC@ChelseaFCLet's go. 👊#LukWhosBack10:50 PM · Aug 17, 2021673405631Let's go. 👊#LukWhosBack https://t.co/5ar5GhgMvDChelsea signed Romelu Lukaku for a club-record fee of £97.5 million this summer as they desperately needed a striker. The Blues were keen on getting Thomas Tuchel the players he wants to challenge for more trophies this season.When Lukaku debuted against Arsenal and scored, it seemed like the missing piece in the Chelsea puzzle was found. However, he has found the back of the net in just one game post his debut. That was a double in a 3-0 win over Aston Villa at Stamford Bridge.The Belgian has been out injured for the last few games. But a return of three goals in eight Premier League games is below par for a player like him. Lukaku will now be looking to hit the ground running and get on the scoresheet a lot more.Tuchel is likely to switch to a 3-5-2 to accommodate Lukaku and Werner in the team and that could help Lukaku a lot.