The injury, which occurred in the ninth minute of the game, made the Portugal striker doubtful for this weekend's game against Celta Vigo and perhaps even the Champions League final.
According to CNN, Ronaldo appeared to leave the field as a precautionary measure with a hamstring strain before his teammates were forced to settle for a frustrating point against a resilient Valladolid.
The report mentioned that Ramos, who has scored five goals in his past four games, unleashed a fine free-kick from 25-yards which flew into the net and it came as little surprise when Humberto Osorio headed home Marc Valiente's corner with five minutes of normal time remaining.
The result leaves Real, which began the game without the injured Gareth Bale, four points adrift of leader Atletico, who face Malaga on Sunday before a final day showdown with Barcelona
The loss of Ronaldo, who has scored 31 league goals this season and 50 in all competitions, will be of greatest concern to manager Carlo Ancelotti, the report added.