M'Vila signed for Sunderland on loan for the entire 2015-16 season.
M'Vila, 28, joined Sunderland from Russian side Ruban Kazan on loan until the summer of 2016 in August 2015, and instantly became a crucial member of the Sunderland side.
He made 40 appearances in all competitions for Sunderland, as the 22-time France international looked to get his career back on track. But Sunderland opted against signing him permanently.
M'Vila was out of contract in the following January at Kazan, but was earning a whopping £100,000 a week (Chronicle). Kirchhoff believed Sunderland made a mistake in failing to land him permanently.
"Well, that was just the start of the problems really. It was a huge decision not to sign him," Kirchhoff said. "He had such a huge impact on our game. Maybe it wasn’t an obvious impact, but as a teammate I felt him missing [when he left].
"Him leaving made a huge impact and I felt the quality went down when he wasn’t in the team. Yann was a cornerstone to our success. He’s an outstanding talent."
A tough-tackling midfielder, M'Vila has since left Kazan in January 2018 and joined St. Etienne where he has got his career back in track as a first-team regular - clocking up 45 appearances for Les Verts.
Sunderland were relegated in the season after M'Vila left, and are now in the third tier of English football while M'Vila continues to shine in the top tier of French football. Kirchhoff, meanwhile, is with second-tier German side Magdeburg.
Have something to tell us about this article?