The 33-year-old Scottish centre-back started his current campaign in pre-season in July 2012 with Birmingham City and has essentially played through both the English Championship and MLS seasons.
Toronto manager Ryan Nelsen reckons Caldwell has played some 60-plus games — with just nine days off. It has been such a long grind that the MLS club has started to give him some days off to recover.
"I love playing football and I love going out and playing matches," Caldwell said cheerfully. "I think my body probably needs a rest . . . it's just getting a little bit difficult to go out there on the training field for me. I feel a little bit achy and sore. But I'm thoroughly looking forward to Saturday (against the Chicago Fire.)
"Everything's new to me (in MLS). I get to go to a fantastic new city that I've always wanted to visit."
A workhorse, the fiery Scot has been one of the bright lights in another dim season. And Caldwell has relished life in North America.
"He has to be one of the best if not the best signing this club has made," said assistant coach Fran O'Leary. "He's a terrific professional, a terrific player and a better human being.
"The influence he's had quickly on the field and in the dressing room has been unbelievable. I think you just have to look at the improvement in the young players around him. They'll be the first to give him a bucket-load of credit. So we're delighted."
Opposition coaches have also been quick to cite the TFC captain in post-game get-togethers, said O'Leary.
"They'll all mention Steven Caldwell."
Toronto — coming off a bye week — faces another tough test Saturday away to the Chicago the Fire (13-12-7), who currently occupy the fifth and last playoff spot in the East with 46 points. But only three points separate the third-place Houston Dynamo (48 points) from the seventh-place New England Revolution (45 points).
Wins are desperately needed to lock up post-season berths.
The Fire have made the most of struggling opposition in recent weeks, defeating FC Dallas and D.C. United on the road and tying Montreal at home. After Toronto, Chicago will wrap up the regular season in New York.
Toronto (5-16-11) closes out its campaign at home to the slumping Montreal Impact, another team desperate for points in a post-season push.
"The playoffs is where we want to go and we want to go soon, not take a long long time," said O'Leary. "We'll be aiming to make the playoffs next season and this gives the guys a little taste of playoff intensity."
Caldwell joined Toronto on loan in early May, making his debut May 18 in a loss to Columbus. A changing backline has not helped matters but there has been an improvement
Toronto gave up 15 goals in 10 games before his arrival. Since then the club has yielded 31 in 22 games.
Caldwell has started 21 of those contests — missing out on the other due to suspension. — playing in all but four of the 1,890 minutes those games covered.
Canadian youngsters Ashtone Morgan and Doneil Henry have flourished beside Caldwell. And fullback Mark Bloom has made the most of his starts.
Caldwell directs traffic from the back and isn't afraid to get in the face of anyone who crosses him. His wagging finger in the face of a rival player is not an unusual sight on the pitch.
Away from the field, Caldwell is lauded for his positive influence on the team. A well-dressed man, he also ups the team's fashion sense.
And he brings oodles of experience.
Caldwell, who has won 12 caps for Scotland, began his pro career with Newcastle United and also spent time at Blackpool, Bradford City, Leeds United, Sunderland, Burnley, Wigan and Birmingham City
Goalkeeper Stefan Frei steps in Saturday for the suspended Joe Bendik, marking his first MLS start since Sept. 24, 2011.
It will be Frei's 82nd league appearance for Toronto — and likely his last. Having lost his starting job, the Swiss-born 'keeper is likely to be deemed surplus to requirements after his US$200,000 contract expires at the end of the season.
Toronto has played 69 MLS games since Frei's last start.
The club continues to talk up Frei, however.
"Stefan's a No. 1 'keeper," said O'Leary. "He could play for any team in this league. It's just unfortunate that he's lost his spot through injury and then Joe Bendik's come in and been arguably one of the top 'keepers in the league this season. Joe's level of consistency has consigned Stef to the bench."
Quillan Roberts, 19, will likely be the No. 2 goalkeeper. Chris Konopka is still recovering from an earlier knee injury.
Fullback Richard Eckersley will likely remain in the cold. He too is headed out the door due to a $300,000-plus contract, with Bloom expected to get another start.
Jeremy Hall is also suspended with fellow midfielders Bobby Convey (ankle) and Darel Russell (muscle strain) question-marks. Convey is more likely to play than Russel, however.
With Matias Laba still recovering from a toe injury, Toronto is not flush in midfield.