The short version is "not very much".
The long version is that we should expect a few loans, including confirmation of one fairly big one: Marco van Ginkel to AC Milan, which still hasn't been made officially official but is all but done regardless. Van Ginkel would represent the outgoing foreign player which Jose Mourinho has been promising for several weeks, leaving Chelsea in not much need of movement other than finding loan clubs for some of the prospects, with Islam Feruz and Nathaniel Chalobah looking as though they're likely to be sent out before the deadline.
Obviously the club might do with strengthening at both centre back and central midfield -- despite the explosive start to the season, we've been wobbly without the ball and have yet to have a wholly convincing match -- but if Chelsea really thought that reinforcements were urgently needed one would have to assume that they'd already have been sounded out. Never rule anything out, but the days in which we'd drop £75 million in transfer fees on deadline day are probably over.