The two sides will square up again on Saturday in the second leg of their MTN8 semi-final at Dr Molemela Stadium.
The first leg at Lucas Moripe Stadium ended in a 1-1 draw, which means a goalless draw would eliminate SuperSport from the competition.
"Ja look there's no doubt Celtic are a good team you know, they showed that over the weekend," Grobler tells snl24.com/kickoff.
"I think that [against Pirates] they rested a few players as well I'm not 100 percent sure but that's what I've gathered. But ja Celtic are a very difficult team, they are very compact at the back. I mean they play with three big centre-backs and they make it very difficult for teams.
"I think Celtic are a good team when they are at full strength. So ja I mean we know what we need to do. The last three seasons we played the first round at home and we drew all three of those games 1-1 and 2-2. So we know what we need to do to get a win in the second leg, we've done it the last three years and ja we trust ourselves to go there and do the job.
"I think we will stick to our game plan, we won't just go there and change much, we believe in what we do. I think [Wednesday] it was a good performance from us. A little motivation-booster for us so obviously we need to stick to our game plan. I mean we haven't even got time to prepare for this game."