Bayern Munich great Ze Roberto believes Cristiano Ronaldo will hang up his boots before the age of 40 following a drop in performance over the last few years.
In his first season back at Old Trafford, Ronaldo, 37, started the campaign well by scoring eight goals in his first 15 league appearances, while he also played a key role in helping United navigate their way into the Champions League knockout rounds.
However, the goals have dried up since the turn of the year as he has found the net just once in his last 10 matches in all competitions.