The French international now says that he has injured his ankle but does not yet know what the exact problem is.
"The problem is I don't know what the injury is," said Gallas. "That's to say I have a sprain, although it might be more serious.
"I've had the results of examinations but they're not sure.
"I know nothing and I prefer to leave myself some days, at least until the weekend, to see exactly what the injury is."
Gallas said he had no option but to play on against Besiktas but was frustrated he hobbled around the pitch.
Many media sources have been sharpening their knifes, expecting Chelsea to sack Claudio Ranieri. This Gallas has added fuel to this, with many people blaming Ranieri for forcing Gallas to continue on. However, this was not the case, and Gallas had this to say to clear it up.
"I asked to return to the field even though there was nothing I could really do."
"I could not run and only touched two or three balls which were headers on a cross. I felt almost useless."
"I had a bad tackle which took my ankle and it turned."
Chelsea face Middlesbrough on Sunday afternoon in the 2pm Pay Per View match. Bolo Zenden will not be allowed to face Chelsea, as he is only on loan from them, and Joseph Desire Job is also out for Boro.
Chelsea's only injury worries are Emmanuel Petit, Celestine Babayaro and obviously William Gallas.
Claudio Ranieri won't be losing too much sleep over this. He will certainly make changes from the midweek team, with Gallas and Babayaro certain absenties.
Chelsea From:
Cudicini, Johnson, Desailly, Terry, Bridge, Gronkjaer, Veron, Lampard, Duff, Mutu, Crespo, Babayaro, Makelele, Cole, Geremi, Hasselbaink, Gudjohnsen, Melchiot, Ambrosio.
Ah, poor Ranieri, what will he do with Petit, Babayaro AND Gallas out??!! He'll just HAVE to play England internationals John Terry and Wayne Bridge, and resort to giving Claude Makelele a run out!