City staff discovered the suspicious package on the tennis courts at the facility, and called police.
Employees do safety checks of all outdoor recreation facilities each morning, the city said in a press release.
A second safety check of all outdoor and indoor recreation facilities was underway Monday afternoon, as recommended by the Royal Newfoundland Constabulary.
Witness Xihue Chen told CBC News he brought his son to a tennis lesson at Wedgewood Park in the morning.
Chen said one of the instructors found the device wrapped in black paper about the size of a beer bottle.
"We went over and took a look at it, [saw] something sticking out of the black paper, it looked like a fuse," Chen said. "We thought it was a bomb."
Chen said the bomb squad was called in, and he left.
RNC Const. Suzanne FitzGerald said the police department's explosive disposal unit used a robot to remove the device.
She said it was disposed of in a safe location.
In a statement before Monday's regularly scheduled council meeting, St. John's Mayor Dennis O'Keefe called the discovery "frightening."