Steven Pienaar could be set to miss further matches after picking up an injury in training, manager Roberto Martinez has revealed.
The South African midfielder was absent for Saturday's 1-0 victory over Chelsea and may not return in time for next weekend's trip to West Ham United.
Arouna Kone also sat out the win over Jose Mourinho's men after sustaining a knee problem, though Martinez expects the Ivorian to make a rapid recovery.
Martinez told evertontv: "I think Steven Pienaar is going to be a little bit longer - it's a grade one soft tissue problem. But Arouna Kone shouldn't be too long."
Matchwinner Steven Naismith and debutant Gareth Barry both impressed having come into the side against Chelsea and Martinez is confident the Blues have the strength in depth to cope with injuries to the squad.
He added: "It's not about who's missing, it's about who's going to be on the pitch. Creating that competition is going to be vital for us to be competitive across the season and I couldn't be happier that we had two influential players missing today and we had other players come in and perform and give their all for the team."