As reported before, Rusev recently underwent shoulder surgery (believed to be on 3/9) and the prognosis is that he will be sidelined for approximately two months.
He has needed the surgery for a while but tried to work through it but reportedly could not go any longer, which is unfortunate for him as he will miss WrestleMania which is the biggest payday for the talent.
This explains both why Rusev he was beaten so badly at Fastlane by Big Show and also why his program with Jinder Mahal was broken off quickly without much of a storyline or feud.
Source: Wrestling Observer Newsletter. Subscription information & prices available at f4wonline.com