"I had a look at him on Thursday and Friday and didn't think it was that much of a gamble to fling him in," boss Gordon Chisholm told BBC Scotland.
"Maybe I was wrong since he got sent off and gave away a penalty. It was an eventful day for the boy."
Sansara made 27 appearances for Walsall in League One before being released this summer.
"He's big and athletic and this gives us a chance to have a look at him," added Chisholm.
"Because he's coming up from England we can't field him as a trialist, so we had to offer him something."
Source: BBC Sport
Source: BBC Sport