Manchester City's win at Old Trafford on Monday has kept alive their slim hopes of retaining the title but it would still require a staggering sequence of results for United to lose their advantage.
"We're a little worried," Valencia told Ecuadorian radio station Sonorama. "Last year, we were eight points with six games to go and we lost the league. Now it is 12 games and seven points, and we don't want it to happen again."
Three wins and a draw from their final seven games would be enough, and three of those remaining matches are at Old Trafford, with relegation-threatened Aston Villa and a Swansea side seemingly cruising towards the end of the season amongst the visitors.
United visit Stoke on Sunday, with a trip to West Ham to follow on Wednesday.
Victory in those matches would leave the Red Devils within touching distance of a record 20th championship, with Valencia eager to play some part after making only a fleeting appearance as a substitute against City.
"They're the manager's decisions, but I was still a bit upset," said Valencia.
"In such an important game, to be not taken into account as a starter was upsetting."
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