Wound after Tumor removal

We took our Great Dane to the vet due to a very bad tumor he had on his side, he was operated a few days ago to remove the tumor but the wound looks terrible and the whole area looks very swollen, he is very uncomfortable. Must we take him back to the vet or maybe to a different vet? We are very worried about our doggo 😞 Any advice would be appreciated. This is how the wound/area looks now.

Hello!  In general we always advise going back to the vet who did the surgery, because they understand what happened at the time and are best placed to deal with any complications.  With the best will in the world, all cases behave unexpectedly sometimes. It may be that where the lump was removed from, left a potential space under the skin (eg a gap between two layers of tissues such as the fat and the skin, which were once separated by the lump) and then tissue fluid (the fluid between the cells) moved into that gap during the night.  After all, it is at a low point in the body and water moved under gravity.  If that is the case, your vet may opt to leave well alone and allow the lump to go down on its own accord, or they may place a drain, but if there is blood or infection there, then they may need to intervene.   Best of luck and please do let us know what was found.