"They beat Adelaide in a playoff game to make it into the main draw of the ACL and Adelaide went on to win the A-League," Janjetovic told The World Game.
"And while they may not be doing so well in the Chinese Super League at the moment, we didn't do so well in the A-League either.
"The Champions League and the domestic competitions are two different things and sometimes teams perform well in one and not so well in the other. The thing you've got to take most notice of is their best form and that's what we'll be doing with Shandong."
Janjetovic's comments are borne out by the fact that while Shandong are in 12th place after seven rounds of the 16-team CSL, they are still alive in the ACL. On the other hand, Guangzhou Evergrande are leading the CSL but have not made it past the group stage in the ACL.
Guangzhou were in Sydney's group. They beat the Sky Blues 1-0 in China on the final night of the group-stage games on Tuesday, but paid for poor results early in the tournament and finished third of the four teams.
Shandong finished second to powerful Korean team FC Seoul in their group.
Adelaide were at home to Shandong in the playoff game back on February 9, but got into trouble in the first half and trailed 2-0. The Reds dominated the second half, but could only pull one goal back and went down 2-1.
"We all watched that game at the time," Janjetovic said. "Look, they're going to be dangerous when we play them. Every team that is still in the Champions League is there for good reason. It doesn't matter if they might not be doing well in their local league.
"We only finished seventh in the A-League, but we've recently focused on the ACL and Shandong have obviously got plenty of focus on the ACL as well at the moment.
"We can't go there thinking 'this is going to be an easy game, we're just going to take the points and come back home'. We've got to give them the respect they deserve or we'll come home with nothing. We have to treat it like it's a grand final and leave nothing out there."
Sydney will travel to China for the first leg of the round of 16 tie, to be played on May 18. The return leg will be played seven days later at Allianz Stadium.
Janjetovic said that after returning home on Thursday morning the team trained on Friday and will have the weekend off before resuming training on Monday.
"We can't take our foot off the pedal, we have to keep working hard," he said. "It's tough mentally just training day in, day out, with no game for two weeks, but we're getting used to that now.
"We have to go to China prepared for anything. We'll watch videos of some of their recent games and try to pick up on their weaknesses and they'll be doing the same thing with us. Hopefully, we can steal the points and put them on the back foot going into the return leg.
"After making the A-League grand final last year it was a bitter pill to swallow for everyone here when we didn't make the finals this year, but we've sat down and reflected as a team on what went wrong for us and where we could be better.
"Most people expected us to not get out of the group stage of the ACL, but we've really gelled as a team in these games. We're trying to correct the wrongs from the A-League and make it pay off in the Champions League."