Ipswich boss Mick McCarthy has offered a short-term contract to former West Ham midfielder Jack Collison.
Chairman Fawaz Al Hasawi has vowed to strengthen Nottingham Forest year on year, with loan arrivals possible.
Humphrey is entering the final year of his contract at Deepdale after joining the club on a free transfer from Motherwell last summer.
The 26-year-old impressed with Preston last term, helping them reach the play-offs only to lose to Rotherham in the semi-finals.
The Jamaica international caught the eye as much for his defensive displays as the attacking prowess that he has always been known for.
The likes of Burnley, Wigan and Leeds are all believed to be keeping tabs on the former West Brom youngster as they look to add pace to their sides next season.
Preston are keen to keep hold of Humphrey, but could face a fight to keep hold of him with clubs higher up the Football League taking an interest in his services.