The baby seal, thought to be around six to 12 months old, was rescued after showing up at the front door of riverside pub the Old Lock and Weir, in Hanham, Bristol on Sunday.
Bar manager John Jefferies, 41, helped rescue the pup, nicknamed Neoprene, who had been tagged in Scotland on June 21.
The British Divers Marine Life Rescue Service was then called to the scene to take care of the pup who was dangerously underweight.
His records show the last time he had been observed, he weighed 30kg and is now down to just 14.8kg.
Neoprene is now in the care of RSCPA West Hatch in Taunton, Somerset.
The pup may have to be taken into a wildlife sanctuary because he was 'not doing that well on his own', but pub workers plan to adopt and sponsor him if that happens. Some workers had joked that he had been making a bid to escape Scotland’s coronavirus rules.
Mr Jeffries said: "In the morning at around 11.30-ish, I was on the bar and our chef came in and said 'we have a baby seal on the slipway'.
"I went to have a look and lo-and-behold there was a baby seal.
"We're right on the river so there is a slipway outside to get boats in and out the water.
"He was making his way up to the gate at the top of the slipway and we contacted the RSPCA trying to get advice on what our next steps were.
"We wanted to stop him coming up to the gate because we weren't sure if he'd fit and there is a road on the other side.
"The advice from the RSPCA was to try turn him around and get him back into the water.
"Fortunately, the tide was going out and when he jumped back into the water he seemed to disappear at speed so we assumed that was the end of that.
"By around 12.30pm he'd come back and obviously it was busier so nobody had noticed it.
"He'd come up the slipway, straight under the gate and then when we spotted him again, he was right outside the pub.
"We contacted the RSPCA and they gave us the details for Marine Rescue.
"They asked if we could try and contain it and they would come and collect it.
"That is easier said than done in a very busy pub, we had a lot of people outside.
"Outside the pub just before you go in there is a wall and a fire escape so we managed to herd him gently into that area and put some barrels across, using them to keep him in.
"We added additional water into that area to make it as wet as possible and got some wet towels and put those down and put those on his back.
"Marine Rescue took him to West Hatch and they found he was underweight - they know he was 30 kilos when he left Scotland and he had halved that on the journey.
"They were able to identify that he wasn't doing that well on his own and wasn't catching the amount of fish he required.
"They're feeding him up and seeing how he gets on and they'll make a decision about whether to release him into the wild.
"He may go to Gweek Seal Sanctuary in Cornwall but we're hoping he doesn't. If he does, we're going to sponsor and adopt him as a pub.”