The gold medal and grand slam winner was warmly congratulated on Twitter after announcing plans to marry in the summer after the Wimbledon tournament.
Murray, 26, was responding to a question from a fellow tweeter asking him when he was tying the knot, to which he replied: "We are getting married just after Wimbledon, should be a great day."
But, after a flurry of congratulatory tweets and press reports, the Scottish star backtracked, writing "3 things.. I don't smoke grass, I'm not getting married (yet) and I don't want to kill Rafael Nadal.."
Murray's faux marriage announcement had the potential of reaching almost 2.5 million people who follow him on Twitter.
Ms Sears, an artist, regularly takes a seat courtside alongside Murray's parents Willie and Judy when he plays.
She accompanied the 26-year-old to Buckingham Palace last October when the Duke of Cambridge presented him with an OBE.
The Scot has spoken fondly of his girlfriend in the past and has said their relationship works well because she ''really understands'' his sport.
The couple have been dating for over eight years except for a short break after they moved in together.
During Wimbledon last year, Murray said Ms Sears, daughter of tennis coach Nigel Sears, copes well with the strain placed on their partnership by the demands of his career.