He played for Strømsgodset, Rayo Vallecano, Lorient, Columbus Crew SC, and Vålerenga, and also spent time with Manchester City, Eintracht Frankfurt, and AGF.

After playing youth football with Sporting Club Accra, Abu signed for English side Manchester City on 31 August 2010.

[4] Abu appeared as an unused substitute in the Norwegian Football Cup Final against Follo, as the club won 2–0.

[25] On 21 February 2014, Abu joined Norwegian side Strømsgodset again, this time on a permanent deal and signed a four–year contract with the club.

[28] Abu played in both legs of the club's first ever UEFA Champions League match against Steaua București, as Strømsgodset lost 3–0 on aggregate.

[32] After the match, manager Bjørn Petter Ingebretsen criticised Abu's sending off, saying the player "was tackled in the leg, he was on the ball, and he bleeds like that.

[36] During a 2–0 win against Rosenborg on 30 October 2016, Abu suffered a knee injury and was substituted in the 19th minute, in what turned out to be his last appearance for the club.

[38] On 24 January 2017, Abu moved to America, where he joined Major League Soccer side Columbus Crew SC as a Special Discovery Player.

[39] He made his debut for the club in the opening game of the season against Chicago Fire, playing 76 minutes before being substituted, in a 1–1 draw.

[42] He helped Columbus Crew qualify for the 2017 MLS Cup Playoffs, where the club reached the Conference Finals, losing 1–0 against Toronto FC on aggregate.

[47] He made his debut for the club, starting the whole game, playing in the defensive midfield position, in a 3–0 win against Tromsø on 19 August 2018.

[49] After joining the club, Abu quickly established himself in the starting eleven, playing in the defensive midfield position.

Following his loan spell at D.C. United, his contract with the club was terminated on 18 December 2020 and he announced his intention to return to play in America.

[62] He made his international debut for Ghana on 8 October 2011, as part of 2012 Africa Cup of Nations qualification against Sudan, and replaced Derek Boateng in the 75th minute of a 2–0 victory for the Black Stars.

[63] Although Abu had appeared just once in qualifying, he was included in Ghana's provisional squad for the 2012 Africa Cup of Nations on 15 December 2011.

[65] He made his debut in the tournament, coming on as a late substitute, in a 1–0 win against Botswana in the group stage on 24 January 2012.

[68][69] According to Tom Vernon, the founder of Sporting Club Accra, he described Abu as "always been confident both on and off the field, always with a smile and a good mood.