Wawrinka leads their previous meetings 3-2. The last one was in January 2011. Wawrinka won in straight sets on a hard court. they have never met on clay.
Wawrinka won the French Open title in 2015 and reached the semi finals last year. He has not lost a set so far in this tournament.
Monfils has also not lost a set so far. He was playing well against Gasquet in the last round. They had shared two tight sets when Gasquet retired after being broken in the 3rd set. His serve was being very effective and he had won 77% of 1st serve points. He was getting over 70% of first serves in court.
I think Monfils can take a set today but Wawrinka wins. Back Waw if he gets broken or loses set 1.