26-year-old Jan Budtz has joined from Danish Super League club FC Nordsjaelland.
Doncaster make double Danish swoop
"I am delighted to join a club with great potential and a new stadium coming," said Budzt.
"I think it is a great opportunity to show what I can do in one of the best leagues in the World."
Also coming in is Tonny Nielsen, 21, who arrives from Viasat Sports Division club Fremard Amager, he stands at 6' 7''.
These are Penney's second and third swoops of the summer, following the arrival of Wrexham centre-half Stephen Roberts.
Penney had said at the start of pre-season that he planned to make ten summer signings as Doncaster look to make a promotion push, following excellent tenth-placed finish last season.