Sam Warburton came off with a knee injury during 12 days before the British and Irish Lions squad is announced.
Warburton, who captained the Lions on their last tour in 2013, scored the Blues’ first try before hobbling off.
Speaking after the game, Blues head coach Danny Wilson said the former Wales captain would undergo a scan.
“He had a bang to his knee. We’ll get a scan and have him assessed as soon as possible,” Wilson said.
Warburton’s Blues team-mates George Earle, Taufa’ao Filise and Blaine Scully were also forced to leave the pitch because of injuries in the first half against Ulster.
Wilson added: “The others [injuries] are bangs that will take further assessment before we know what they are.”