On 4 March 2012, in a match against Roda JC, Sulejmani was seriously injured after 30 minutes. Two days later the Ajax medical team has determined that he would have to undergo surgery to the meniscus, going on to miss the rest of the season. In February of the following year, it was reported that he was set to join S.L. Benfica as a free agent; after this was confirmed, coach Frank de Boer demoted him to the reserves, where he remained until the end of his tenure.