The Gunners have been chasing Lemar all summer but are not thought to be close to striking a deal.
Monaco want big money for the Frenchman, and Man Utd have reportedly now joined the Gunners in the chase for his signature.
It was claimed yesterday Jose Mourinho has turned to the French midfielder as he looks to make a fourth signing before the end of the transfer window on August 31.
And United fans are excited by the prospect of snapping up the Monaco star – and getting one over on London giants Arsenal in the process.
“Arsenal fans must be bricking it right now”
Man Utd fan talks Thomas Lemar to Old Trafford
“Arsenal fans must be bricking it right now,” one fan teased on forum Red Cafe.
Another supporter added: “I don’t see this happening, but I would love it just for the Arsenal fans reaction.”
A third posted: “He’s a weird one for me. I don’t really want us to sign him as I don’t see how he’ll fit in without drastically reducing Martial and Rashford’s minutes.
“But I also don’t want Arsenal to sign him.”
An Arsenal fan said letting Lemar slip through their fingers would be the final straw.
He posted on Twitter: “If Manchester United sign Thomas Lemar, I’m not watching an Arsenal match until Wenger leaves.”
Both Arsenal and United have until 11pm on August 31 to seal a deal for Lemar before the transfer window closes.