Johannesburg - Kaizer Chiefs head coach Steve Komphela believes Mamelodi Sundowns will struggle to defend their Premiership title due to their commitments in the CAF Champions League.Sundowns will do battle in the continental cup competition when they face Enyimba in Nigeria on Tuesday, the same day that Amakhosi kick off their Premiership campaign with a trip to last season's runners-up, Bidvest Wits.The Chiefs boss also highlighted the fact that he expects several other sides in the Premiership to challenge Sundowns for the domestic title, after strengthening in the off-season."It's going to be very tight," Komphela told Sowetanlive. "Sundowns are campaigning in Africa and it's not going to be easy to maintain such performance."At some stage fatigue and lack of interest will creep in. There's going to be a stage where players will say we are sick and tired of training."Those who did not achieve last season will try [to] work harder to achieve something. There's just a whole lot of different scenarios, but we have to concentrate on our own scenario, where we say let's take these 30 matches as 30 cup finals."It comes with a lot of concentration and consistency."When asked which areas he felt his team could improve on in the upcoming campaign, Komphela added that he expected to see his players take more responsibility for their performances."You cannot shy away from that," he said. "Expectations are clear. You have to win matches and win trophies. Being number two is not good enough at Chiefs."