Bath Rugby Union have signed van der Giessen and Fernandez-Lobbe in a double deal. Lobbe, 35, who has 60 international caps and has played in three World Cups, joins from Northampton Saints for the rest of the season.
Van der Giessen, 28, who spent last season with Top 14 side Albi, has signed a three-month contract. Bath were forced to seek reinforcements after an injury to Scott Hobson.
Head coach Steve Meehan said: “Both players will be a valuable addition to the squad at this time when we have injuries in the second row.
“They are both experienced players, who have played in a variety of leagues, and have really good attitudes.”