And although the Portuguese was forced off with a leg problem towards the end of their quarter-final first leg victory, manager Carlo Ancelotti stressed it was just a niggle.
CHAMPIONS LEAGUE TOP SCORERS SEASON-BY-SEASON
- 2013-14: Cristiano Ronaldo (Real Madrid) - 14 goals
- 2011-12: Lionel Messi (Barcelona) - 14 goals
- 2013-14: Cristiano Ronaldo (Real Madrid) - 13 goals
- 2012-13: Cristiano Ronaldo (Real Madrid) - 12 goals
- 2010-11: Lionel Messi (Barcelona) - 12 goals
- 2002-03: Ruud van Nistelrooy (Manchester United) -12 goals
Ronaldo received treatment on the pitch for what looked like a problem with his left knee, but Ancelotti said: "He was bothered a bit by his knee, we needed to defend and to avoid any risks, we've substituted him. It's not a problem. He isn't injured."
Viva Ronaldo: The Portuguese could surpass Messi's 14-goal haul
Ancelotti added he would not take any chances with the Portugal international.
"We'll see how it goes. At this moment we're not concerned by the niggle. If it continues, naturally we'll rest him but we're not thinking about that because the player is calm.
"There's not a problem at the moment."
Ronaldo has now scored 14 goals in eight games this season and is likely to have three more matches - at least - to surpass Messi and Altafini.
Dortmund striker Robert Lewandowski will return to bolster the depleted German side in the second leg at the Westfalenstadion next week, yet overturning the three-goal deficit is a tall order.