The Austrian turned pro with Mapei in 2001, before going on to ride for T-Mobile, HTC-Highroad, Team Sky, and Dimension Data from 2016.
He had seemed set to retire at the end of the 2018 season after being diagnosed with a serious brain injury, but set off on the comeback trail and signed up for another year at Dimension Data.
With the end of the year now in sight, the 38-year-old is now likely to go one more.
"It would just be for my own thinking, to do 20 years a pro - not many have done that," Eisel told Cyclingnews at the recent Arctic Race of Norway.
"I think I can still contribute a lot tot the team and the young riders. No team would sign me to win a bike race – those days are long gone, but I still enjoy it, and I think that's the most important thing. The injury last year showed me I still enjoy it and I'm not done with it.
"I guess it would be more like one more year and probably a year where it doesn't have to be 100 per cent, with all the races, Tour de France and 20 classics. If I do Flanders or Roubaix and a few other things, for example, then I'm happy. It becomes too all-consuming over the years."
Eisel has not yet started actively trying to put plans in place for next season – nor does he seem overly concerned about doing so.
"I'm not stressing. I'm also not really looking around. I don't have a manager – I do it on my own, and I haven't called anyone yet. At the moment I can't be bothered – I'm just trying to get my legs back and enjoy racing. Then I'll worry later – or maybe I won't worry at all and I'll just retire. It's good when you've done 19 years – you stress less."
What is certain is that he won't be with Dimension Data in 2020.
"It would definitely be something new," he said. "There's no space for me here anymore."
Eisel joined the South African team in 2017, linking up with his old HTC teammate Mark Cavendish and taking up the role of road captain. However, his relationship with Dimension Data management appears to have become strained this summer since the squad for the Tour de France was announced.
The headline news was that 30-time Tour stage winner Mark Cavendish did not make the cut, but Eisel felt similarly aggrieved at being left at home. "I definitely wasn't happy with that," he says.
Eisel acknowledges that he "probably didn't fit into the team", but also explains that fitness was a factor in his selection. After the Tour of California in May, he started getting headaches, which understandably caused panic given last year's brain injury. It turned out the headaches were linked with a shoulder and neck strain, along with over-exertion in a hectic first few months of the season.
"Of course, when you have something like I had last year, you start freaking out. I ran from doctor to doctor and it was completely sideways. You can't really see that sort of thing on an MRI scan, so went to see osteopaths – two different ones that I trust, and they both said the same thing. When they tell you it's definitely not neural, that it's nothing to do with the brain, it's all good."
Still, Eisel lost three weeks of training time and ran out of time to prove his condition for the Tour, even if he suspects there was more to the decision than that.
"I was definitely really disappointed. I think I would have been ready for the Tour. You can look at the numbers and everything. I know myself, and my body knows what it has to do in the July over the years. I think I would have been ready there, but it just didn't happen," he said.
"Not everyone can be happy – you see that all the time in teams. The management make decisions and you can fight it but at the end of the day… I ended up being at home and my third child was born on July 15. We have a little daughter again – Greta – so that all puts it into perspective. It's not all about cycling."
As for Cavendish, a close ally over the years, Eisel vouches for his claims that he was in the right sort of shape to justify his inclusion, but stops short of saying it was an error to leave him out.
Cavendish has suffered with Epstein Barr virus in the last couple of years and hasn't won a race since February 2018. However, he declared he was free from the virus in May and Dimension Data director Rolf Aldag openly contested team manager Doug Ryder's decision, arguing not just that Cavendish deserved a spot on reputation alone, but that he was in good enough shape to win a stage.
"Mark was with me in Austria, we did motor pacing and he looked good. It was promising," Eisel said.
"Of course there's a lot of personal pride and everything in there. At the moment, I think we're no closer to knowing if it was the right decision, because normally you know more when it's done. It happens."
In the end, Dimension Data came away from the Tour with little to celebrate, Giacomo Nizzolo's fourth place finish on the opening stage arguably being the high point.
"They definitely tried – it's not like they went on holiday – but I guess the boys didn't enjoy it that much not being that on top of the game," Eisel said.
Cavendish returned to racing at the Ionica Adriatica on July 25, but abandoned on the second stage. He then went to the Tour de Pologne but pulled out after stage 5 to head to the Netherlands to work for Chris Lawless at the European Championships.
Eisel was with him in Italy and Poland, and insisted that the 34-year-old is on the right track to returning to his former self.
"What he came back from, that needs time. It's not enough to train 100 per cent; you have to do a little bit more to come back to the old level," Eisel said.
"He got a crack again from not being in the Tour, so of course he didn't ride his bike too much either. He's also just a human being – you get that kick and it's hard to refocus. Ionica was the first race back and that didn't go really well. Poland was looking really good and now he's focused on the next races. He showed character and strength at the Europeans for the GB team.
"People already said many times that he lost it. I think he wants to prove it, to himself and the people who keep telling him he's not good enough. That's what drives him, and of course he wants to win a bike race again."