The 26-year-old Scotland international has returned to light training after specialists diagnosed the cause of continuing pain as a hairline fracture of the fibula he broke earlier in the campaign.
Thomson is one of a series of midfielders currently on the injured list, although it could be several weeks yet before manager Tony Mowbray has a full complement from which to choose.
Andrew Taylor and Mickael Tavares could return to the squad for Saturday' npower Championship trip to Millwall as they battle their way back from hamstring and toe injuries respectively.
Willo Flood is back in training after dislocating his kneecap in the opening game of the season, while Rhys Williams is also close to a return from the pelvic condition which has hampered him for much of the last year.
Source: PA
Source: PA