The mammal was first spotted in the River Clyde on Tuesday
Marine experts attempting to rescue a whale in the River Clyde in Glasgow have said they are "not confident it can survive".
British Divers Marine Life Rescue (BDMLR) said the whale was in bad shape and may have to be "put to sleep".
Vets are uncertain what species the mammal is because only its back and fin can be seen.
Rescuers believe it is a northern bottlenose but said the creature may also be a Risso's dolphin.
Efforts to rescue the five-metre long mammal have been ongoing since it was first spotted in the Clyde on Tuesday.
Alan Knight, chairman of BDMLR, said: "Northern bottlenose whales feed on squid off the continental shelf and they cannot find that around the Clyde or the UK coast.
"The chances are that if it is very weak it will try to come out and rest on a mudbank, and then we can go into action.
"We are not confident it can survive. With its current body condition we fear it may have to be put to sleep but if on inspection it is in better condition we will try to do something to save it."
Northern bottlenose whales can grow to 12 metres long.
They follow a migratory route through the Atlantic Ocean from Scandinavia, along the west coast of the UK to Nova Scotia in Canada.
A northern bottlenose whale was seen swimming off the Dorset coast earlier this month but washed up dead on a beach in Bournemouth on Monday night.