Baseball: New York Yankees pitcher Masahiro Tanaka floored by Giancarlo Stanton line drive

Frightening scenes have marred the opening day of New York Yankees pre-season camp, with star pitcher Masahiro Tanaka struck in the head by a line drive.

The Japanese native was alert after the horror blow, but was rushed to hospital with serious concerns about a potential concussion.

Tanaka was pitching to power-hitting batter Giancarlo Stanton, when the rocket shot was launched back towards the mound.

The right-handed pitcher failed to duck the blast, and was immediately floored and seen cradling his head. 

Tanaka stayed down for several minutes, before medical staff hurried him off the diamond and into an emergency vehicle.

The Yankees said Tanaka was responsive and walking under his own power. He was sent to New York Presbyterian Hospital for further evaluation.

Stanton was forlorn, crouching down in the batter's box, with his head in his hands immediately after the incident.

A reduced 60-game Major League Baseball season is set to get underway later this month.