The Gunners are without a number of key players for their match at the Emirates Stadium, while Blues star Juan Mata returns to his former club for the first timeChampions League action is upon us - and Goal.com is the place to be if you want all the updates as they happen.
Our LIVE! service brings you team news, fan views, goal flashes, red cards and match reaction - all in one place.
We can bring the action to life on your computer - from how Arsenal line up at home to Olympiakos, to whether Juan Mata receives a good reception on his return to Valencia.
Click on the link below and you can follow all the matches this evening:
As well as bringing you updates from the Emirates Stadium and on Chelsea’s trip to Valencia, we will keep you up to date with the rest of the Champions League fixtures taking place, including Barcelona’s match away to BATE.
With reaction coming in from around Europe, Goal.com will bring you the best of what the managers and star players have to say on the games within moments of the final whistle.
No matter who you support, you'll get all the news and views you need right here throughout the evening.