According to the Football411.com website, Amakhosi enter the tie at the top of the standings, although they only hold a one-point lead over second-placed Orlando Pirates, who host SuperSport United on Wednesday.
Barker's men were in impressive form before the break, unlike their midweek opponents, who only just climbed out of the relegation zone before the festive intermission.
"We have to double our efforts," Mosimane told the media ahead of the midweek clash at Loftus Stadium.
"It is almost like playing a national team. Six of their players were regulars during the Nations Cup.
"I'm fighting for credibility at Sundowns and we have a long way to go."
Mosimane took charge of the Brazilians in December last year with the club languishing in the drop zone, and has helped turnaround their fortunes.
However, he is acutely aware that it was Chiefs who had the upper-hand when the two sides met earlier in the PSL campaign with a 2-1 win.
"I watched the tape, and the one where Sundowns won 4-1 (in the MTN8 quarter-finals) and I realised we have a big game on our hands," the former South Africa mentor added.