The 20-year-old, a half-back or first five-eighth, was a guest of the NZRU at last Saturday's 30-13 All Blacks victory in the Bledisloe Cup against Australia.
And Tew admitted the youngster may make a move home when his contract expires at the end of the current Australasian season.
Tew said: "We have made inquiries with Benji to see what his intentions are at the end of the year and offered him an open invitation to come and talk to us if he's considering a return to rugby union as an option - that's as far as it has gone.
"But the first thing I have to make clear is that Benji is contracted till the end of the year and we are aware of that and we certainly wouldn't be doing anything in breach of that.
"He's had a great year for Wests Tigers and the guys that we rely on to spot talent have spotted him - and they (players) have to be very good to do that."
Marshall, born in the North Island coastal town of Whakatane, made his NRL debut in 2003 and has scored 12 tries to date this term, guiding his side into play-off positions.
Wests offered Marshall a lucrative three-year contract last month, but this year's Tri-Nations series may prove his final outing in the 13-man code.