Bacterial cellulose (BC) is a suitable drug delivery carrier owing to the nanofibrous micro and mesoporous structure. One of the unique aspects is the tunability of BC microstructure by the addition of certain additives in the growth medium during the synthesis of cellulose by bacteria. In the present work, BC was in situ modified by adding Polyethylene glycol 2000 (PEG 2000). Effect of in situ modification on crystallinity, chemical composition, microstructure and morphology and, porosity was studied by XRD, FTIR, SEM and BET, followed by the effect on drug (Diclofenac sodium) loading and release kinetics. As a non-incorporating in situ modifier, PEG2000 increased the overall porosity, pore volume and decreased the specific surface area with no significant effect on crystallinity. In vitro, drug release studies revealed that a huge burst release for PEG modified BC as compared to pristine BC. The mechanism of release is further investigated by mathematical modelling. This work opens up avenues of exploring the wide possibility of tuning immediate and sustained drug release from bacterial cellulose for various release applications. © 2021, Indian National Science Academy.