It was almost a year ago that Thomas Tuchel's European champions took to the field at the Emirates. It was sunny, the game was on TV and Chelsea blew Arsenal away. It looked easy, for them and their new signing Romelu Lukaku, who scored the first goal after 15 minutes.

Now, things are different for Chelsea, off the pitch and on. Lukaku is back in Milan spouting once again his favourite lines about proving himself, showing his quality and reminding everybody how good he is.

The fact is Lukaku has now played for two big Premier League clubs - Chelsea and Manchester United - and failed at both of them. So, yes, we know exactly how good he is. 

Back in London, Chelsea will officially unveil the forward who Tuchel hopes will fill the hole left by Lukaku and Timo Werner, whose surprisingly poor two years at Stamford Bridge have been ended by a return to Germany.

Raheem Sterling faces a lot of pressure to provide Chelsea's main attacking threat this season

Welcome, then, Raheem Sterling, a player who most certainly is good enough for the toughest league in European football, having proved that at both Manchester City and Liverpool.

Tuchel will be asking a lot of Sterling. The load he will carry this season will be heavy.

As it stands, Chelsea do not have a reliable and functioning centre forward on their books and to expect Sterling to paper over that void on his own already feels from the outside like a little too much.

On signing the 27-year-old for just south of £50million earlier in the summer, Tuchel described Sterling as 'horrible to play against' and added 'he is exactly what we need to raise the level of our players'. No pressure, then.

None of this will faze Sterling, who has met greater challenges in life than this. However, he has never carried this responsibility before. 

At Liverpool the standard bearers were Steven Gerrard and Luis Suarez. At City they were Sergio Aguero, David Silva and Kevin De Bruyne.

It must be remembered that City let Sterling go without a fight, and to a Premier League rival at that. How often does this happen? And when it does, what does it say?

We know that Sterling's relationship with City manager Pep Guardiola was sometimes tense, but that in itself is not unusual. Guardiola tends to live on the edge with his players and every so often one of them topples off the precipice. 

Even so, Guardiola and his ally Txiki Begiristain do not think they have sold a transformative player to Chelsea. If they did, they would not have done it.

So Sterling's progress in London will be fascinating. A year ago, it was easier to see a path forward for Chelsea and it had Lukaku at the front of it. Now? Things look less clear. Chelsea will doubtless be competitive up to a point. They have many good players and a fabulous coach.

But who scores their goals? It seems a lot to ask Sterling to do that on his own. His best Premier League return to date is 20, while playing in a much better team than this one.