Definerely a serious injury. He was serving much slower than usual, on average (a few good serves do not change the average).
Obviously, not the most serious kind of injury (i.e. the ones that force you to retire from the match), but serious enough to put you in a position incompatible to reach your best level. Injured Nadal can beat Fritz, not Novak. To have a chance against Novak, you can't have an andominal inury that makes you serve like a WTA player (exaggeration, but you get my point, his serve is severely damaged).
It's official. Nasal has a 7 mm abdominal fracture as per his morning medical test in London:
Mucha expectación por ver la sesión preparatoria de Rafael Nadal de cara a la semifinal de mañana con Nick Kyrgios. El tenista balear, que lleva una semana sin ejercitar su saque e
www.marca.com
But yeah, according to his haters, Nadal cannot be injured.