 However, Mumuni tore his anterior cruciate ligament in March 1996 during pre-season and was injured for the whole season.Umea were relegated in that season and spent the rest of Mumuni's spell at the club in the Division 1 Norra, finishing third, second and seventh from 1997–99.Among Mumuni's teammates at Umea were defender Erik Sandvärn and fellow Ghanaian, Shamo Quaye, a midfielder who also played for Hearts of Oak and Ghana.