Chelsea coach Antonio Conte has been impressed with his side's pre-season preparations but says there is still work to be done defensively.
West Ham visit Stamford Bridge on August 15 in Chelsea's Premier League curtain-raiser, with Conte targeting seven days of graft to get his team on the same page at the back.
After defeating Werder Bremen 4-2 in a friendly, ex-Juventus boss Conte was left displeased by his side's defensive lapses.
Nemanja Matic gave away a penalty to allow ex-Chelsea striker Claudio Pizarro to convert from the spot, before substitute Lennart Thy was given the space to power an effort home from range in the second half.
"There were some bad situations to concede two goals which I didn't like," Conte told Chelsea's official website.
"We must improve a lot, but we were tired after our pre-season, it was a good victory.
"We've finished our pre-season, it was very tough and hard in all aspects and we must be pleased to finish with a win.
"We are working very hard to be ready, it will be difficult, we know we have some problems but we are trying to solve them.
"I saw positive things and many situations that we can improve. We are working on this. Now there is only one week left of work before the season starts."