Karanka's relationship with some of his senior players has been well documented, and he even had a mid-season sabbatical form the Riverside following a heated team meeting.
Jose Mourinho's former number two has been made favourite for the Valencia job following Gary Neville's sacking, and the hot-seat at the Mestalla would be an attractive proposition for the Spaniard.
Following a disappointing 0-0 draw at home to Ipswich Town on Saturday, the Teessider's currently find themselves second in the Championship table, level on points with leaders Burnley and third-placed Brighton & Hove Albion.
Boro host the Seagulls on the final day of the season in a game that could turn out to be a promotion decider.
The North East club have won six of their last eight games, but back-to-back draws have halted their progress.
If Middlesbrough do achieve promotion to the Premier League, surely it will be too good an opportunity for Karanka to walk away from, but a return to his native Spain cannot be ruled out for obvious reasons.
Next up for Boro is a tricky trip to Birmingham City before the all important final game against Brighton at the Riverside.