Should Petr Cech go to Arsenal, Jose Mourinho would want more than just cash in return. The Gunners haven't had a world class goalkeeper in quite some time, and despite Cech being pushed out of the number one role at Chelsea by the arrival of Thibaut Courtois, the Czech star is certainly better than the gaggle of morons currently on parade at the Emirates, and would make Arsenal correspondingly more dangerous next season.
You can therefore understand why the manager would be so keen to get something back -- say, an Alex Oxlade-Chamberlain or another of that ilk -- should Cech move to London's second fiddle this summer. But according to the Telegraph, the Gunners are refusing the inclusion of any 'key' players* as they negotiate with the Blues over the goalkeeper. Which makes sense too, since they are trying (bless their little hearts) to catch us, not fall further behind.
*Not that player exchanges are by any means common.
Despite the Chelsea hierarchy being willing to let Cech have a say in where he ends up, the club still has a strong hand here, since they're by no means obligated to sell. If Arsenal don't want to play our game, we certainly don't have to do business. And really, I'd hope that we don't.