While Irish international Brennan basks in the glory of Toulouse's European Cup final victory last month, Thomas' season has stretched into its 11th month.
Potentially, there are still three games to go - all against New Zealand in Christchurch, Wellington and Auckland.
And Thomas is determined to stay mentally and physically strong for the biggest challenges in his career, starting with Saturday's first Test at Jade Stadium.
Thomas had already won a European title and a Six Nations Championship, complete with Grand Slam, before his French club commitments finally ended and he could join the Lions in New Zealand, albeit almost two weeks late.
But a try-scoring Lions debut against Wellington was enough to clinch his Test place, ensuring a possible fairytale finish to the longest campaign Wales wing Thomas has known.
"Trevor is on holiday in France, and he's ringing me from the side of his pool, sipping lager!" said Thomas, of his close friend and colleague.
"It's night-time over here when he rings, so I am freezing cold in my bed and he's lying by the side of a pool!
"It has been a really long season for me, and come the end of this trip, I will take a deserved break.
"I've played more games this season than I have ever played in one season in my life.
"But the fact I am tired just goes out of the back of my mind. I am getting good rest in this week, with the chance to get fresh for Saturday's Test," he added.
"It's not only about keeping your body fresh, but keeping mentally fresh as well.
"The season started for me last August, and it has been a rugby ball nearly every day, so it's keeping my mind fresh and waking up every morning, still wanting to go out there and train.
"But when you come to an environment like this one, there are enough quality players around you, it's kind of refreshing. It's still rugby, but with different people."
Thomas, Wales' record international try-scorer with 34 touchdowns during an 83-cap career, is optimistic about the Lions' chances.
"There are so many guys around you that are such quality players, they can mould and adjust to each other," he said.
"Yes, we are not the perfect team at the moment and it is going to take a while because we have come from so many different backgrounds, so many different clubs and so many different ways of playing.
"But when we do click, it will be great. I haven't had much trouble fitting in with any style of play, but not because of me, more because of the guys around me.
"I trust the guys and I rely on them - I know they are world-class players."