No, Tzavellas is not a decent option neither as a CB nor as a LB. At CB position Sokratis, Manolas and Retsos (injured atm) are locks while Papadopoulos' team got relegated and himself is injured again. The 4th spot should basically go either to Siovas who's been starting in Spain with Leganes, or to Mavropanos but he won't be starting with Arsenal this season. Under these circumstances I'd call up Oikonomou who's a starter in AEK as a replacement for injured Retsos and Mavropanos because we should take care of our future backline.
In LB; we do have PLENTY of BETTER options than Tzavellas. Tsimikas is already miles better than him offensively and when he gains some experience he'll manage to be a great modern full back, like Vrsaljko to say. We also have Lykogiannis who obviously does better than Tzavellas as well as Torosidis, Stafylidis and Mpakakis who can play in both LB and RB.
In reality Tzavellas should even be an option, let alone atm that he's a free agent, but you never know with Skibbe as a coach. I bet he will get called up, so will Tziolis instead of Galanopoulos. I unfortunately can guarantee you that, despite Galanopoulos should be already a rotation player in this team.