Rawson is undergoing the concussion protocol after a clash of heads during last week’s defeat at Swindon saw him taken to hospital as a precaution.
Cooper has brought in six players during the January transfer window and hopes to sign up to three more before the end of the month.
However,Callum Evans and Fabien Robert have been loaned out until the end of the season to Macclesfield and Aldershot respectively.
David Amoo is absent for Cambridge with a further hamstring problem.
Midfielder Amoo came on as a substitute in last weekend’s goalless draw with Mansfield, but was replaced himself after 10 minutes.
Striker Jabo Ibehre is available following the completion of his three-match suspension.
Southampton remain in the hunt for Red Bull Salzburg's Amadou Haidara and are reportedly readying a £15million offer.
Aston Villa are reportedly weighing up a summer move for out-of-favour Huddersfield defender Michael Hefele.
Southampton are lining up a summer bid for Huddersfield Town midfielder Aaron Mooy, reports claim.
Rangers manager Steven Gerrard is weighing up a move for Liverpool full-back Jon Flanagan, reports claim.
Scottish champions Celtic are reportedly ready to offer full-back Calvin Miller a new deal before sending him out on loan.
Everton target Jack Wilshere has sparked a scramble for his signature after confirming he is leaving Arsenal this summer.