A troublesome right ankle saw Real Madrid's David Beckham come off four minutes from the end of his club's 1-1 draw at Osasuna.
The England skipper left the fray with coach Carlos Queiroz anxious not to take any chances ahead of next week's Madrid derby against Atletico.
Former Marseille man Ibrahima Bakayoko put Osasuna into an 11th-minute lead but Ronaldo equalised with a crisp low shot 16 minutes from time as Real escaped with a point to avoid a third league defeat of the season.
It was the Brazilian World Cup winner's 10th goal of the season but it came against the run of play against a team who had won this fixture for the last two seasons.
"It is an important point," said Ronaldo. "All points are good to take."
Real were a shadow of their usual selves as, even prior to Beckham's premature departure, they were missing injured 'galactic' trio Zinedine Zidane, Luis Figo and Roberto Carlos.
The point moves them provisionally top of the table with 27 points from 13 games, a point clear of Deportivo La Coruna while Osasuna stay in fourth place.
Deportivo play host to Villarreal on Sunday and put their recent spate of poor form behind them with a 3-0 win in the Champions League over AEK Athens on Tuesday.
Meanwhile, Real Sociedad twice surrendered the lead as they were held to a 2-2 draw at Murcia.
Igor Gabilondo, who found the net in the 2-2 Champions League draw at Olympiakos in midweek, opened the scoring in the 29th minute but Murcia, second from bottom in Spain, hit back two minutes after the interval through Luis Garcia.
Inside a minute, Sociedad, who were without influential Turkish midfielder Nihat Kahveci, were back in front courtesy of Oscar de Paula but Murcia refused to give up and hit their second equaliser of the night with David Karanka finding the net in the 68th minute.
"It's a shame. Again it's a missed opportunity," said Sociedad coach Raynald Denoueix.
"We could see victory but we lost two points. It's necessary to be able accept the result."
Meanwhile, a minute's silence was held before the match between Atletico Madrid and Malaga in memory of the seven Spanish intelligence officers who were killed in a terror attack in Iraq earlier Saturday.
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