With Dani Carvajal picking up an injury during the first leg in Munich last week and Nacho still not fully recovered from a muscle tear, many have tipped head coach Zinedine Zidane to use Vazquez as a fill-in right-back in Tuesday's second-leg instead of trusting his youngsters.
However former Madrid coach Valdano believes it will be a big ask for the 26-year-old to maintain his focus and discipline for the full match.
He said: "Lucas Vazquez doesn't have the work-rate or sacrifice you have to have to be a right-back. The other day he played there for only a few minutes, but 90 is something else".
Although Valdano also argued that Vazquez will "leave nothing on the pitch as he always exceeds what he is asked".
Turning his attention to the match as a whole, he added: "Real Madrid have their ups and downs, so although the 2-1 is good, it's not definitive".