The 22-year-old moved to the Premier League outfit from Barcelona in August 2011 and is now tied to Jose Mourinho's side until 2017.
Romeu made 16 top-flight appearances in his first season at the club, but a knee injury hampered his development.
Since then the Spaniard has found his first-team opportunities at Chelsea limited, leading to a loan spell in La Liga with Valencia last season.
He has subsequently returned to England for pre-season training with Chelsea and played over 70 minutes in a 5-0 friendly victory over Wycombe Wanderers on Wednesday.
Romeu has represented Spain at under-21 level and played for his country at the 2012 London Olympic Games.
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