Sangare made a deadline-day switch to Forest, with Steve Cooper’s side determined to bring in a defensive midfielder in the summer.
The Ivory Coast star established himself as a midfield cornerstone at PSV and Cooper is also hoping to see significant contributions from him moving forward.
PSV are due to take on Arsenal in the Champions League this week and will not be able to call on Sangare.
And De Mos highlighted his concerns over whether PSV will regret their decision to let Sangare go this summer during the match, especially if they get dispossessed.
“The football that Arsenal play, I saw them against Everton, is not that great”, De Mos told Dutch daily the Eindhovens Dagblad.
“It is not that they create an abundance of chances. PSV will play a very good match there.
“And I even believe in a good result.
“The midfield is quite good.
“The only question is whether they will miss Sangare because there will be moments when you lose the ball.
“But they have good positional insight, especially Schouten.
“He can surprise with the ball.
“There are few English teams, except for Brighton, who have such a good positional game as PSV at the moment.“
Arsenal are clubbed with PSV, Lens and Sevilla in the Champions League this season and they are eyeing making an impact on the elite continental tournament.