The Uruguayan striker netted just 10 league goals in 63 appearances in a frustrating two-and-a-half years with Sir Alex Ferguson's side.
However, since leaving Old Trafford the 29-year-old has re-established himself as one of the most lethal front-men in la Liga, netting 54 league goals in 104 outings for Villarreal and a further 48 in 69 for present club Atletico Madrid.
His 32 league goals for the rojiblancos in 2008/09 earned him both the Pichichi trophy as top-scorer in la Liga, as well as the Golden Shoe for being the deadliest marksman in Europe - trophies he also picked up as a Villarreal player.
The likes of Liverpool, Tottenham Hotspur, Manchester City and Barcelona are now being linked with his signature.
And Forlan says he is glad he left England when he did, putting his lacklustre form down to the stiff competition for places he faced at the time.
“The competition was hard at Manchester, there was Van Nistelrooy, Yorke, Cole, Giggs and Solskjaer,” he said.
“I only appeared for 10 minutes every time. That is why I moved to Villarreal, who were not the club they are today.
"I left United to revive my career and this challenge proved a good decision.”
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