Henderson is suspended for the Champions League quarter-final second leg at the Etihad Stadium after picking up his third caution of the competition proper in last week's rousing 3-0 victory at Anfield.
Wijnaldum - usually deployed further forward by Jurgen Klopp - was selected at the base of the midfield in Saturday's 0-0 draw at Everton to give him a taste of things to come against Pep Guardiola's side.
And the Netherlands international is ready to step into the breach as Liverpool aim to reach the last four for the first time in a decade.
"The manager was trying it in pre-season and he said it might happen in the season," Wijnaldum said.
"He said at that time that it could happen that I will play in that position and he might look to do it in the future. Now that time has come.
"Normally, I stand higher on the pitch but in this position you get more on the ball, you have a lot of moments. When you play one position ahead, you have less moments.
"You are more responsible because you are the second or sometimes the first man in the build up. You are quite an important player in that position as well."
Henderson is confident his absence will not be felt in a crunch clash with City.
The Reds skipper said: "Gini was brilliant in that position against Everton. He got on the ball and kept moving it. He showed he can play there. Hopefully he can do the same job for us again on Tuesday night."
Klopp, meanwhile, has been fulsome in his praise of a man who has started 22 Premier League games in 2017-18.
"He is creative, he is good with the ball, he can pick the pass, he's good with that stuff, he has a good view of the play - it is all there that you need," the German coach said.
"He can jump to the roof! He is really physically strong and so that is a really good position for him, but yeah, we had two days training - kind of! - and we can not constantly train with 11 v 11 to give him the opportunity to get used to that position."