Chesterfield assistant manager Lee Richardson has warned David Bridges that he has his work cut out in landing a contract at the Spireites.
Bridges is looking to prove his worth at Saltergate
The 21-year-old Cambridge midfielder's trial at Saltergate has been extended after he impressed in the first week.
But Richardson said: "We may not have an immediate vacancy but we need to be aware of players who could do a job if required later in the season."
Bridges has already turned down a new contract offer at the Abbey Stadium.