Davies was making his return to the side against Oldham after missing three games with an arm problem but unfortunately he had to be substituted after only 17 minutes when he pulled up sharply while chasing Jonathan Forte to a forward pass.
The influential central defender was replaced by giant Scot Gary MacKenzie.
Speaking directly after the Oldham win, Parkinson admits it wasn't easy to tell the exact damage caused by the defender just yet but he was left fearing the worst.
Parkinson said: "It is a big blow for us.
"It is his hamstring but we won't know the full details until we have proper checks on him - it didn't look go though.
"When it goes like that and it is a sudden injury, normally it is unfortunately bad.
"We will be expecting the worse so anything better than that will be a bonus.
"Gary MacKenzie was top class after Davo's injury though. He was very professional in his play and faultless when he came on."