Matsatsantsa were expected to challenge for the Premiership title this season, but have seen that dream fade after only winning twice in 12 matches since losing the Confederation Cup final to TP Mazembe in November last year.
SuperSport are now fighting for a top-eight finish so that they can defend their MTN8 crown next term.
Tinkler, who also guided Orlando Pirates to the Confed final in 2015 and assisted Roger de Sa when Bucs reached the Champions League decider two years prior, explained how competing on the continent takes its toll.
"We get back here and we have to catch up league fixtures," said Tinkler.
"What happened to us is you got to sit and play 10 league fixtures in the space of 30 days, and we expect these guys to bounce back every three days and put on the same performance, the same energy, the same level of concentration.
"That's not easy, that's extremely difficult. And then a lot of the time we talk about depth, but yeah depth doesn't really help. It's all about form. Players need to be playing on a regular basis to gain form. So if you are chopping and changing week in and week out there is no form. There is no stability, there is no consistency.
"And also you are facing that issue as well when you look at the amount of injuries we been having, the amount of suspensions. Morgan's [Gould] in, Morgan's out, this one's in, that one's out, and to create that consistency becomes very difficult."
United trail pace-setting Tshwane neighbours Mamelodi Sundowns by 13 points, and next host struggling champions Bidvest Wits at Lucas Moripe Stadium on Saturday (20h15).