I would imagine that motivation of many players already exists.
Those coming to the end of their contracts and needing extensions or moves must surely want to impress MA or any other interested manager respectively.
Those with longer contracts, I would hope, will want to keep themselves in MA's plans - or catch the attention of other managers.
Those on loan should want to do impress MA in order to secure a bid in the summer - or be wanting to impress their own manager, or, indeed, the managers of other clubs should a move elsewhere be in the cards...
I suspect that Southend was contributed to by lack of practice together as much as anything else , which should be resolved by time together on the training ground.