Since Michael Douglas will be playing Hank Pym, the first Ant-Man before Paul Rudd’s ‘Scott Lang’ will be his successor, he would be likely to wear the ‘Ant-Man’ suit and maybe fight side by side with Lang.
However, according to the veteran actor that his costume “will be hung up” meanwhile Paul ” will be wearing it in good form.”
“Paul Rudd is ripped,” he told MTV, “He’s been training and working out for this picture for a long time. He was so cut, that they had to soften his costume up, with all the built-in six-packs and all of that.”
Source: Comic Book Movie