Colback was a fairly regular starter for Newcastle last season, as they earned promotion to the Premier League.
However, Benitez has decided to be ruthless with his squad - with a number of players set to depart.
Newcastle could offload a whole host of their squad, who Benitez has deemed could struggle in the Premier League.
And Colback has reportedly been made available, after failing to convince the Spanish boss.
Colback is yet to fully win over the supporters at St. James’ Park, after a series of middling performances.
Colback has added steel to Newcastle’s midfield, but there are question marks over his ability in possession.
And with Newcastle likely to strengthen in midfield over the summer, Colback’s position in the team is now under threat.