He competed at the 2006 World Junior Championships in Athletics in Beijing the following year, but did not get past the qualification round.

[4] He represented Qatar at the 2007 Pan Arab Games in November and won a silver medal behind Salem Al-Anezi, with a jump of 2.17 m.[5] A few months later, he returned to action with an appearance at the 2008 Asian Indoor Athletics Championships in his hometown.

The high jump gold went to Sergey Zasimovich but Al-Mannai still reached the podium, taking the bronze medal.

[3] After a year out from competition, Al-Mannai returned by setting a personal best of 2.27 m in Malmö, which earned him an appearance at the 2010 IAAF Continental Cup.

It was a surprise win over 2007 World Champion Donald Thomas and marked the first high jump medal and victory by an Asian at the competition.