Despite fielding only four players who are guaranteed a start in the opening 2015 World Cup qualifier against the Faroe Islands next month, the Scots almost snatched a win had Suzanne Malone's injury-time goal not been ruled offside.
The Serbs went ahead in the 29th minute through Danka Podovac and Signeul said: "We showed great patience on a pitch which wasn't suited to our passing game. I am very curious to know why the second goal wasn't allowed by the referee because Suzanne is certain she was onside."
Signeul rested goalkeeper and captain Gemma Fay to give much-needed game time to her deputy Shannon Lynn. That left just Rachel Corsie, making her international return after 10 months out with injury, Hayley Lauder, Jo Love and Jane Ross as automatic first choices.
The 20-year-old Clelland, making only her second international appearance, found the target 15 minutes after coming on.