The manager has signed the midfielder after completing the paperwork on Wednesday.
Saints are down to 14th in the National League South table and Allinson knows the festive period will be crucial to getting their play-off push back on track.
They play Eastbourne Borough on Saturday and the former Concord Rangers, Ebbsfleet and Braintree man will be in the squad.
The St Albans boss thinks Sanderson is over his injury issue.
“Jordan was with Concord Rangers last season and injured his cruciate, but he’s come back from that and is looking to play at this level again,” Allinson told the club’s website.
“He’s impressed us in training so far and we hope that he can bring something different and his arrival gives us more options going into the Christmas period.”