City have taken midfielder Simon Heslop on a week-long trial from Championship side Barnsley.
Heslop, 21, came through Barnsley's youth ranks but has played only once for the first-team, against West Brom on the last day of the 2006/07 season.
At the start of this season he joined Grimsby on loan, making eight league appearances for the Mariners.
Heslop is set to play in the Imps' reserve match against Nottingham Forest on Wednesday.