Chelsea manager Graham Potter said forward Raheem Sterling has been through a challenging phase at the London club following his move from Manchester City but backed the England international to deliver more.

Chelsea signed Sterling from City for about £47.5m ($57.3 million) in July but his performances have been underwhelming with six goals in 21 games in all competitions this season.

Sterling will face his former club City in the Premier League on Thursday at Stamford Bridge before the teams meet again in the FA Cup at the Etihad Stadium on Sunday.

“It’s been a challenge for him but it’s been a challenging period for everybody,” Potter told reporters on Wednesday, as his team sit 10th in the table, 11 points behind second-placed City.

“There’s been a lot of change and a lot has happened, so in that regard, it’s not easy to completely settle or hit the ground running.

“There is more to come from Raheem I’m sure but he gives his best every day and we need to help him get to the level we know he can reach.”

Chelsea have won only one of their last seven league games and were held to a 1-1 draw by lowly Nottingham Forest on Monday.

Potter, who took over in September after Thomas Tuchel was sacked, described City as a “fantastic” team.

“We have to play well ourselves, that is the key. Then you have to understand the quality they have and try to stop it. It sounds simple when you condense it down but the reality isn’t so straightforward,” he said.

“They are a top team but we can cause them a problem.”

Goalkeeper Edouard Mendy will remain sidelined as he recovers from a shoulder injury sustained playing for Senegal at the World Cup in Qa tar.