Robinson spent time at Brighton and on loan at Aldershot in 2009
Torquay United could potentially face Football League sanctions for fielding an unregistered player during Tuesday's League Two home match against Hereford.
Striker Jake Robinson, 24, who arrived in a loan deal from Shrewsbury until the end of the season on 31 January, is believed to be the player involved.
Torquay manager Paul Buckle told BBC Radio Devon: "I was shocked. It's not the sort of news you expect.
"It's extremely disappointing. It's not a nice feeling."
Robinson scored on his debut for the Gulls in the 3-1 home defeat by League Two strugglers Hereford.
We are all gutted over what has happened and all we can do is apologise and we'll wait and see what happens
Torquay United manager Paul Buckle
Buckle continued: "Jake put us in front and one of our directors came down to the dug-outs and said they had some bad news.
"I worried about my family to start with because it's quite a surreal moment.
"Then I found out Jake should not have been playing for us and I was shocked.
"We are all gutted over what has happened and all we can do is apologise and we'll wait and see what happens," Buckle added.
In a statement the club said it was alerted that an unregistered player had taken to the field after kick-off and have voluntarily offered an explanation to the Football League.
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