(CNN) -- Six Nations champions Wales are sweating on the fitness of star center Gavin Henson as they begin their defense of the title against Scotland at Murrayfield on Sunday.
Henson has been in fine form for the Ospreys this season ahead of the Six Nations.
Wales completed a grand-slam clinching win over France in the 2008 season, the last time injury-hit Henson played for them in a Test.
Coach Warren Gatland was hopeful of pairing Ospreys standout Henson and Cardiff Blues center Jamie Roberts for the first time, but a tight calf may put paid to that.
Henson did not train on Wednesday and will be assessed for fitness on Friday.
It is his latest injury problem after ankle and Achilles problems last year limited his appearances.
"Gavin just felt his calf tightening in training," Gatland told Press Association.
"He will have some treatment, there is a day off tomorrow, and when he comes in on Friday we will make a decision."
Gatland said that if Henson does not make it, Tom Shanklin will come in to partner Roberts with Andrew Bishop brought in as a replacement.
Henson's scheduled return is one of three changes from the side that beat the Australian Wallabies 21-18 in the final autumn Test.
He is due to replace Shanklin, with Roberts moving to outside center, while 20-year-old Cardiff Blues wing Leigh Halfpenny makes his Six Nations debut and Ospreys scrum-half Mike Phillips returns after recovering from a major knee injury that required two operations.
Wales have only beaten the Scots in Edinburgh twice since 1985, while their last trip to Murrayfield two years ago saw them produce a sorry display in going down to a 21-9 defeat.
"The Scots will be looking forward to taking us on," added Gatland. "And if we take the challenge lightly, we will be playing straight into their hands."