Answer
Panionios and Atromitos were the two clubs where Mitroglou had loan spells before becoming a regular at Olympiacos. He spent the 2007-08 season with Panionios, scoring 4 goals in 25 appearances. The following season, he moved to Atromitos, where he netted 15 goals in 33 games. These loan spells helped Mitroglou develop his skills and gain valuable experience, which paved the way for his success at Olympiacos.