Sukar, 21, has impressed manager Gary Mills during an impressive pre-season trial.
Born in Hartlepool, Sukar started on the books at Middlesbrough and Sunderland and joined Dundee United in August 2015.
After loan spells at Peterhead and Brechin City, he played twenty-eight games last season for Arbroath who won the Scottish second division title.
Mills said: “He’s been with us for a couple of weeks now – a left-sided centre-half that can operate at left-back if needed.
“He has come in to be part of the eighteen-man squad that we have now put together and he will only get better.
“He wants to do well, he is one of the younger players who will get better by learning from the more experienced players”.