Indeed, Redknapp is amazed at how quickly things have changed for Manchester United star, who has gone from being a regular to a youngster far out of the first-team picture at Old Trafford.
And the Sky Sports pundit believes Memphis Depay's impending arrival at United will complicate things even further for 20-year-old Januzaj.
As such, he insists the Manchester United youngster has some thinking to do ahead of next season.
Redknapp said: "It's amazing how quickly things change in football. This time last year Adnan Januzaj was a Man United regular and a bright hope for the future.
"This season he has barely featured. With Memphis Depay now joining the squad, the young Belgian has a big decision to make this summer."
|Chances Created||Shots On Target||Appearances||Minutes Played|
|Ángel Di María||51||18||26||1,619|
|Robin van Persie||27||37||26||2,085|
As Opta stats show, Januzaj's Manchester United season in numbers doesn't reflect too well on the 20-year-old.
Louis van Gaal has given him just 783 minutes of Premier League football, which has amounted to just 15 chances created and only five shots on target.
Granted, Ashley Young has only hit two more shots on target than Januzaj during far more minutes - but the winger has been far more creative and has generally been on top form this term.
As Redknapp mentions, meanwhile, the signing of Depay won't make things any easier for the youngster at Manchester United. Should he stay or should he go?