The worldwide break arrived at the most inconvenient time for Chelsea manager Antonio Conte.
The Spain global has been on four yellow cards since the 3-0 defeat to Arsenal, and has not picked up any warnings, which will lead to an immediate suspension.
Chelsea Manager Antonio Conte has heaped praise on Diego Costa.
While manager Antonio Conte said Costa was now back in training after pulling out of worldwide duty for Spain in midweek, he suggested there was ongoing concern over his striker.
"He must continue that, working in this way, with his commitment and work rate".
"Costa had a bit of an injury after the game with Everton".
Costa has scored nine Premier League goals in eleven appearances for the club this season and has played a major role in their recent run of form.
The Spain global will be joined by Belgium's Eden Hazard in the squad to face Aitor Karanka's men.
Middlesbrough, on the other hand, haven't had the best of times since returning to the Premier League this season after a space of ** years. The same for Eden. It's important to put these players in the best condition for their talent and for me it's important to see that they put himself, their talent, in the team. He's an example for all.
The Blues' fine form continued prior to the global break with a 5-0 home win against Everton - a match in which the striker scored - and they travel to play Boro on Sunday. "For me, Oscar is an important player in the squad".
Antonio Conte has expressed his respect for former Chelsea midfielder Frank Lampard but says he can not offer him a job on his staff while he is still an active player.
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"This system, this formation, I think is a good fit for this squad".
"Oscar's future is Chelsea".
Like Conte, Karanka is enjoying an upsurge in fortunes after three games unbeaten for Boro culminating in their hard-fought 1-1 draw against Manchester City at the Etihad Stadium a fortnight ago.
"They're going to play long balls to find Christian Benteke and we need to avoid all these crosses and long passes as much as possible".
Chelsea have beaten Hull, Manchester United, champions Leicester, Southampton and Everton in the last five Premier League games, since Conte switched to a three-man defence after the loss to Arsenal.