The Chiefs' try-scoring machine Sitiveni Sivivatu is doubtful for their clash against the Lions in Hamilton this Saturday.

The Chiefs backline has been on fire recently, with the All Black speedster scoring six tries in his last two games, which included four against the Blues.

Sivivatu injured his shoulder in the course of "scoring" a disallowed try in the 50-26 romp over the Reds in Brisbane and coach Ian Foster said that he definitely strained his shoulder. The Chiefs' medical staff are also concerned about a possible dislocation.

"It looks like there might have been a bit of movement in his shoulder joint but it's hard to say how bad it is," Foster told the Waikato Times.

"It could be a reasonably significant shoulder injury or it could be a bad strain, but either way he's pretty sore."

Sivivatu underwent x-ray and scans to determine the extent of the injury and it is likely that Sosene Anesi will take his place in this week's line-up.

His absence will be a big blow for the Chiefs as the back trio of Sivivatu, Mils Muliaina and Lelia Masaga has been in rampant form this season.

While Foster is happy with his side's current form he stressed that they need to kick up a gear ahead of a few physical South African fixtures.

"They are playing off a platform that is pretty effective at the moment but we've got some big challenges with the South Africans coming up soon so that's going to be the next step for us up front," Foster said.

"There's no doubt we're going to have to step up. People are going to look for ways to slow down our game and we've just got to be conscious of that and keep improving ourselves."