Robson, 34, was a free agent after leaving MLS side Vancouver Whitecaps this month.
Robson, who also played for Middlesbrough under Gordon Strachan, could make his debut tonight against Coventry tonight.

FORMER Celtic and Scotland star Barry Robson last night clinched a transfer-day deadline move to League Two outfit Sheffield United.
Robson, 34, was a free agent after leaving MLS side Vancouver Whitecaps this month.
Robson, who also played for Middlesbrough under Gordon Strachan, could make his debut tonight against Coventry tonight.
We moderate all comments on Evening Times on either a pre-moderated or post-moderated basis. If you're a relatively new user then your comments will be reviewed before publication and if we know you well then your comments will be subject to moderation only if other users or the moderators believe you've broken the rules, which are available here.
Moderation is undertaken full-time 9am-6pm on weekdays, and on a part-time basis outwith those hours. Please be patient if your posts are not approved instantly.