On 7 September 2002, Addo tore right knee ligaments for the second time, in a 2004 African Cup of Nations qualifier versus Uganda[13] in Kampala.

[14] On 24 September 2003, Addo's career was under threat after he re-injured his troublesome right knee for the third time in Dortmund's 2–1 UEFA Cup victory over Austria Wien.

[16] After sitting out the whole of 2004, Addo returned to action as a substitute in Dortmund's 1–1 league home draw with Borussia Mönchengladbach in the last weekend of January 2005.

On 9 August 2007, Addo signed a three-year contract with hometown Hamburger SV,[18] initially alternating with the reserves and the first team.

Addo was strong in one-on-one situations, physical, creative, and versatile enough to play on both wings, on the inside and also in the central position,[24] although his main skill was his ability to dribble the ball.

[33] On 29 March 2022, he qualified Ghana (on away goals) to the 2022 World Cup in Qatar, after drawing 1–1 against the Super Eagles of Nigeria.

[34] In May 2022, Addo was appointed as the head coach until the end of December 2022 alongside maintaining Chris Hughton as technical advisor and George Boateng and Mas-Ud Didi Dramani as assistant coaches, the same set-up for the 2022 FIFA World Cup final play-off matches against Nigeria.

[35][36] Addo won his first match as manager on 1 June after leading Ghana to a 3–0 victory over Madagascar in a 2023 AFCON qualifiers.

[37] At the 2022 FIFA World Cup tournament, Ghana went on to lose their first match against Portugal by 3–2, however they won their second group game against South Korea by 3–2.

[50] In September 2024, Addo was involved in a car crash along with John Paintsil and Fatau Dauda after their vehicle was damaged as it avoided a head-on collision with a pick-up truck that veered into their lane.

The Ghana Football Association issued a statement shortly after the incident confirming that all three individuals were in stable condition.