The man, who is in his 55s, was taken to hospital with life-threatening injuries after being shot several times inside a gym in the Vasastan district of Stockholm at 12 o'clock on Monday.
The shooter is said, according to sources to SVT, to have been looking for another man, a Bandidos man.
The Mc gang has several conflicts in both Stockholm and Linköping.
Police are investigating the incident as a suspected murder.
No person has been arrested since the incident.