Kim Kallstrom has a back injury and will not play in the next five Arsenal games, Sky sources understand.
Arsene Wenger signed the Spartak Moscow midfielder as a stop-gap on deadline day after losing Mathieu Flamini to suspension and Aaron Ramsey and Jack Wilshere to injury.
Arsenal went ahead with the loan deal in the full knowledge Kallstrom had an injury which would delay his debut.
And the Sweden international is expected to miss games against Crystal Palace, Liverpool (twice), Manchester United and Bayern Munich.
Flamini will return from a ban in time for the FA Cup game against Liverpool and the first leg of Arsenal's Champions League tie with Bayern.
And Wenger hopes to have Wilshere back for next weekend's Premier League trip to Anfield.