Cunningham has enjoyed an outstanding debut season for Preston and has been a virtual ever-present in Simon Grayson's side in the Championship.
The former Manchester City youngster has made 44 appearances in all competitions and played a key role in helping Preston to a successful campaign in their first season back in the Championship.
His impressive form could see him still earn a place in the Republic of Ireland squad for this summer's Euro 2016 finals in France.
Cunningham is entering the final year of his contract at Preston after signing a two-year deal last summer and his suitors are keeping tabs on his situation.
Wolves, QPR and Blackburn are all in the market for left-back reinforcements this summer and Cunningham is thought to figure highly on their wanted lists.
Preston would be loath to lose Cunningham, but they could find their resolve tested to keep hold of the defender this summer.