The 25-year-old has played six matches for the Iron since joining the club at the beginning of October.
Boss Brian Laws said he does not yet know whether Syers will be given permission to play in the FA Cup this weekend.
Laws told the club's official website: "We have agreed with Doncaster to allow him to stay with us for another month.
"We are still in negotiations with them to see if we can play him in the FA Cup next week against Grimsby Town. Hopefully we should know that later on in the week."