First, he must win the players over and convince them that they have a future at the club, former players said.
He then will have to fulfil owner Roman Abramovich's edict - to win Europe's top club trophy twice and make the Blues self-financing by 2013.
'The end of Mourinho's three-year reign will upset the team,' former player Graeme Le Saux said.
'They'll be disappointed, most certainly. Because, over a period of time, they've bought totally into his philosophy.
'All the players that are part of that dressing room core are going to feel a great sense of loss and uncertainty about their future.'
While installing Grant, 52, as coach and retaining Steve Clarke as assistant will help ease the transition, the pair may not be able to bolster morale.
Former player Gavin Peacock told BBC Radio Five Live: 'It's going to be hard to get that team spirit that Jose managed to manufacture.'
Grant is perceived as Abramovich's man, and several players 'lack respect' for his achievements, which include four Israeli league titles with two different clubs.
Keeping Clarke as assistant may prove vital, said Le Saux.
Only four players have spent more time with Chelsea than the 44-year-old, who was promoted to assistant manager when Mourinho arrived.
'From a player's view, continuity is important, because you have an idea of what's expected of you - as a team on the pitch and your role within that team,' he said.
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