[3] Yennaris received his maiden call into the first team squad for a League Cup third round tie versus Shrewsbury Town on 29 September 2011 and he remained an unused substitute during the 3–1 win.

[10] After signing a new contract,[9] Yennaris made two further substitute appearances before joining League One club Notts County on a youth loan in March 2012.

[10] Entering the final six months of his contract,[15] Yennaris departed Arsenal on 27 January 2014,[5] after making only four senior appearances for the club.

[2] On 27 January 2014, Yennaris transferred to League One club Brentford and signed a 2+1⁄2 year contract for an undisclosed fee.

[5] He made his debut in a 1–1 draw at Shrewsbury Town on 1 February,[16] but was replaced by Adam Forshaw after suffering a dead leg on 50 minutes.

[20] Yennaris made his first appearance of the 2014–15 season in a League Cup first round match versus Dagenham & Redbridge on 12 August 2014, but lasted just 20 minutes before suffering a back injury.

[21] After recovering and then suffering a thigh injury in September,[22][23] Yennaris had to wait until 3 January 2015 to make his second appearance of the season, which came in a 2–0 FA Cup third round defeat to Brighton & Hove Albion, when he replaced Alan Judge after 88 minutes.

[25] On 27 February 2015, Yennaris joined League Two club Wycombe Wanderers on a one-month loan,[26] which was later extended until the end of the 2014–15 season.

[30][31] He scored the first senior goal of his career in Wycombe's 3–2 final-day win over Northampton Town,[24] which confirmed a fourth-place finish and qualification for the end-of-season playoffs.

[36] Despite some injury troubles during 2016–17 pre-season and a long-standing calf problem,[40][41] Yennaris was fit enough for a place on the bench versus Huddersfield Town on the opening day and after coming on for Josh McEachran in the second half, he scored his third Brentford goal on 77 minutes, though the match was eventually lost 2–1.

[47] Yennaris lost his starting central midfield place to new signing Kamohelo Mokotjo early in the 2017–18 season,[10][48] but regained it in mid-August 2017 after an injury to Josh McEachran and a personal issue suffered by Ryan Woods.

[2] On 31 January 2019, Yennaris transferred to Chinese Super League club Beijing Guoan for an undisclosed fee.

[59] Yennaris made just three appearances during the 2021 season (again affected by COVID-19) and in November 2021 he was forced to undergo two surgeries in London on an "uncommon" ankle injury.

[65] He made 24 appearances and scored one goal during the 2024 season,[10] in which the club narrowly missed out on AFC Champions League Two qualification.

[10] On 8 January 2025, Yennaris signed a one-year contract with Chinese Super League club Shanghai Shenhua on a free transfer.

[69] Yennaris played in six friendlies for the U19s in late 2011 and early 2012, which were scheduled after the team received a bye to the elite round of the 2012 European U19 Championship qualifying.