A colleague flagged down a passing police car in the street following the incident on Saturday.
Student James Bartlett told the Coventry Telegraph: “I saw him walking backwards and forwards holding his arm with the angle grinder plug dragging behind him.
“I didn’t think anything was up at first but then I saw the blood on the pavement below him.
“He looked OK but then he started to turn really pale which was when I noticed something was up.
“It looks like it had got caught in his jacket or something.
“You couldn’t see where it had cut him but blood was coming out so a friend wrapped a belt around his arm.
“A friend or colleague was on the phone and ran in front of a police car which was going past.
“They stopped and gave help and a couple of minutes later two more police cars came down with sirens on and brought a first aid kit.
“They had him laid down on some grass with a belt around his arm.”
A spokesman for West Midlands Police said: “We were first on the scene at 12.15pm and an ambulance had been called.
“The man was believed to have been working at the university and the incident will be referred to the Health and Safety Executive.”