The 25-year-old has had a stunning campaign with 14 goals in 10 league games whilst he has also claimed four hat-tricks in all competitions.
It is claimed that Liverpool, along with Arsenal, have a major interest along with a host of clubs on the continent.
Now his coach Jose Miguel Michel admits it will be tough to hang on to the 25-year-old.
"We've known for some time that there has been interest from many clubs," he said.
"But that's only logical considering how well he has been doing lately.
"There have been no concrete proposals so far, but if he keeps on doing well, it's going to be hard to keep him."