[14] Romeu's first UEFA Champions League appearance came on 19 October 2011, playing the full 90 minutes in a 5–0 group stage home win against K.R.C.

The statement highlighted that the Blaugrana did not have an automatic buy back clause as first suggested, only having first refusal on any deal if the Blues wanted to sell him in the future.

[17] On 25 September 2012, Romeu scored his first goal for Chelsea, taking a penalty in a 6–0 win against Wolves at Stamford Bridge for the season's League Cup.

[18] Manager Roberto Di Matteo stated that the departures of Yossi Benayoun, Michael Essien and Raul Meireles would mean more playing opportunities for the Spaniard; however, on 11 December, he suffered a knee injury in a game against Sunderland, being sidelined for the rest of the season.

[26][27] He made his debut two days later, as a half-time substitute for Dušan Tadić in a 3–0 home defeat to Everton, earning a booking after three minutes for a foul on James McCarthy.

[28] He scored his first goal for the Saints – and first in a professional league – on 5 December, equalising for a 1–1 draw against Aston Villa at St Mary's Stadium.

[34] On 23 February 2021, he produced “one of the greatest tackles of all time” after he made up a serious amount of ground to prevent Leeds United forward Raphinha from scoring, but the game ended in a 3–0 defeat.

[36] However, he was able to make an appearance on the final day of the 2020–21 season, replacing Kyle Walker-Peters in Southampton’s 3–0 defeat to West Ham United.

[41] He participated in the 2008 UEFA European Under-17 Football Championship with Spain, playing four matches and helping his country to eventual victory in the tournament.

[42] After making his professional début for Barcelona in 2009, Romeu became a mainstay in the under-19 and under-20 national teams, featuring heavily in the 2010 UEFA Under-19 Championship elite qualification round.