Murray, 27, and Ms Sears, 26, are couple since 2005 and she regularly watches his matches.
Last Wednesday it is thought the Wimbledon champion popped the question to Ms Sears.
During a question and answer session with fans Murray, from Dunblane in Perthshire joke that he was getting married after Wimbledon earlier this year.
Murray told his 2.3 million followers about an hour later: “3 things… I don’t smoke grass, I’m not getting married (yet) and I don’t want to kill Rafael Nadal…”
It would appear that Ms Sears, his partner of more than nine years is now proposed by Murray.
The daughter of former Lawn Tennis Association head of women’s tennis Nigel Sears, Sussex-born Ms Sears met Murray at the US Open in 2005.
She was once described by future mother-in-law Judy Murray as “the best thing to happen to Andy”.