British and Irish Lions coach Warren Gatland says it would be an incredible achievement if Wales captain Alun Wyn Jones makes a fourth tour next summer.
Jones, 35, will become rugby's record cap holder when he plays his 149th international - including nine for the Lions - against Scotland on Saturday.
Jones could add to his tally of Lions test appearances should he make next year's trip to South Africa.
"That would be an incredible feat," said Gatland.
Jones and Gatland toured South Africa, Australia and New Zealand together in 2009, 2013 and 2017 respectively.
"I am not sure how long he'll keep going," added Gatland.
"I think he's got ambitions for next year with the Lions. It's a position with a huge amount of quality and depth and that's going be a challenge for him.
"It's important that he has a good Six Nations - he'll know that - but if he does end up in South Africa in 2021, it would be his fourth Lions tour.
"If the form is good enough, whether it is Alun Wyn Jones or Jonny Sexton, they will definitely be in consideration.
"For a lot of those players the autumn is a chance to put their hands up to be noticed and the real criteria comes in the Six Nations because that's when it matters."
Jones may be about to pass Richie McCaw's previous record number of caps, but Gatland does not believe the second row has quite finished.
"It's an amazing accolade to become the world's most-capped player, particularly (coming) from a small nation like Wales," added Gatland.
"He's going to set the bar incredibly high. I don't know how long he can go on for, maybe another 10 or 20 caps.
"We'll wait for that day when he does decide to call it quits and I'm sure we'll celebrate what has been an unbelievable career internationally."
Gatland was Jones' Wales coach between 2008 and 2019.
"I'm not surprised he's reached this milestone," he added.
"He's a player who doesn't often get injured, trains all the time and as he's got a little bit older and matured, he's learned how to manage himself, a lot more so than his younger days.
"Trying to get him to have a rest or a break, he didn't always want to do that. It was almost like a martyrdom thing.
"There's balance now. Once he got married and had children, he's got a fantastic balance between rugby training and home life.
"He's matured incredibly well, is unbelievably respected by the players (because of) the example he sets at training, the high expectations that he has on himself.
"That honesty comes through with his performances. He doesn't hide away from anything and that's why he has so much respect from the players.
"He still never takes the jersey for granted, is still waiting for selection. 'If I'm selected next week' those sort of comments he makes. He respects incredibly the opportunity he's had to play for Wales, he's so proud as a passionate Welshman to have played."
Jones was Gatland's captain late in his Wales tenure after earlier stints by Ryan Jones and Sam Warburton.
"He came into the role late after Sam Warburton, but he's done an incredible job in the way that he's led in his own way," said Gatland.
"He's comfortable having different ideas, challenging others and challenging myself when I was coaching and disagreeing with me. I admire that incredibly.
"I didn't always agree with him, but he's his own man and that's one of the strengths he has brought to that Welsh team."
Gatland believes Jones is lauded on the world stage after being part of a Wales team that won three Grand Slams and reached two World Cup semi-finals, as well winning and drawing Test series with the Lions.
"That recognition didn't come early on even though he was performing well," said Gatland.
"Wales were doing well and his performances for the Lions were good but it's not probably until the last few years he's had that recognition worldwide because of what he's achieved.
"He's an unbelievable competitor. He is well-respected, loved in Wales and admired around the world."