The development comes just a day after Frankfurt board representative Fredi Bobic confirmed their interest in the attacker.
Boateng became a free-agent after terminating his contract with Spanish outfit Las Palmas on Wednesday.
The 30-year-old and UD unanimously stated the decision has been necessitated by the Berlin-born’s desire to return to Germany to “be close to his family”, interestingly, having only signed a three-year contract extension in May.
In unarguably his best time of topflight football, the German-born netted 10 times in 28 La Liga outings last season, finishing as UD’s highest scorer of the campaign.
He won Serie A and Super Cup titles with the Rossoneri between 2010 and 2013.