Different circumstances, but hopefully Costa's response will be as positive as Hazard's for the Chelsea manager.
Chelsea manager Jose Mourinho this week publicly stated that he was unhappy with Diego Costa's fitness, saying the striker needs to work harder on his fitness, and has revealed he will start for Chelsea in their last Champions League group game against Sporting Lisbon at Stamford Bridge.
The Blues boss said: "He has to improve his condition. He was injured and had many doubts because he went a long time without training.
"Obviously that must have an effect on a player in the way he runs, the way he moves and in his co-ordination."
It is not the first time Mourinho has publicly expressed his desire for a member of his team to improve during his second spell back at the club, where he asked questions of a particular attribute of Eden Hazard's game, when it came to helping the side out when defending.
Mourinho said towards the end of last season: “When the comments come from a player like Eden it’s normal because he’s not the kind of player to sacrifice himself for the team.
“He’s not mentally ready to look at his left-back and leave his life for him.”
He was proved right during their Champions League semi-final at Stamford Bridge, where Hazard switched off defensively leading to Atletico Madrid equalising just before half-time. Atleti, helped by Costa, went on to win the game 3-1 and booked their place in the final against Real Madrid in Lisbon, only to suffer heartbreak themselves.
But this season, Hazard's game seems to have reached a new level as he unlocks defences, and if he keeps performing to a high level the chances are he will be amongst the favourites for the player of the year crown.
There seems to have been an attitude change from the Belgian, which was reflected after the Blues hammered Schalke on matchday five of this season's Champions League.
He said: "We were winning 5-0 against Schalke in the 88th minute and Eden Hazard made a sprint to defend. Winning 5-0 at minute 88."
There doesn't seem to be any kind of attitude from Diego Costa to suggest that he won't go the same way as Hazard. Costa's injury problems are well documented but his goal record since arriving in West London shows his desire, though his form has dropped a little in recent weeks. There was one time he reported for training after international duty earlier than initially anticipated - whether that was for treatment on an injury or not was unclear.
It's scary to think that he has been in such impressive form in front of goal and not been at his fittest. Mouriho's comments seem to be an attempt, at least, to get Costa performing beyond the level he is currently at.
They may be different circumstances from that of Hazard's, but he's hoping the same desired effect occurs with Costa.