Complex sentence: In December 2015 he ended his partnership with Raonic and started to work with the World No.3 Roger Federer as assistant-coach with the Swiss Davis Cup Captain Severin Luthi.
Split into simpler sentences: In December 2015 he ended his partnership with Raonic and started to work with the World No.3 Roger Federer. His role would be assistant-coach together with the Swiss Davis Cup Captain Severin Luthi.