The 2.03m centre injured the foot during training last week and missed the Nuggets' game against the Nelson Giants in Dunedin on Saturday night.
Tisby was hoping to be fit for this weekend's derby against the Southland Sharks at the Edgar Centre but was still hobbling yesterday.
Arlidge was waiting to hear what the scan revealed when the Otago Daily Times contacted him last night.
"If it is a fracture, from what I can gather, they can take a while to heal," Arlidge said.
"You need total rest. It could be weeks," he said.
If Tisby has broken a bone in his foot, the Nuggets will need to find a replacement, and soon.
But Arlidge said that was a worst-case scenario and he was hopeful his star would take the court for the franchise again.
If the news is bad, Tisby faces the prospect of an earlier return home, although Arlidge said it was not a given.
"There might be other options yet.
We might be able to find some way to keep him with the franchise."
It has been a tough week or so for the Nuggets.
They slumped to their seventh consecutive loss this season when they were beaten 102-71 by the Giants on Saturday.
To make matters worse, Tisby's fellow American import, Tyler Amaya, is also in doubt for the next game.
He was socialising with his team-mates in the Octagon after the game and was assaulted while trying to catch a taxi home.
The 27-year-old forward was punched in the face and fell backwards, cutting the back of his head.
The laceration required stitches and he was left with a bruised face and a swollen eye.
On Monday, Amaya rated himself a 50-50 chance of playing but Arlidge said it was looking increasingly likely the Nuggets would face the Sharks without their two best players.
"He [Amaya] is still getting headaches and is still very giddy.
He is going to try and do some non-contact stuff [today] and we'll just take it from there."
The Nuggets rely heavily on Tisby and Amaya.
The pair have accounted for most of the Nuggets' offensive production, Tisby averaging 23.5 points and Amaya 20.
The next most productive player on the roster is the captain, Sam To'omata, who averages 6.3 points.
Tisby is also the team's leading rebounder, averaging 10.3, and Amaya tops the assist count with 3.8 a game.
The team is desperate to post its first victory and, if it were to win only one game this year, most of the squad would probably pick Saturday's match against its neighbour as its best chance.
The Sharks, in their debut season, have had three wins from eight games and could have easily won another three, having close losses to the Nelson Giants, the Taranaki Mountain Airs and the Hawkes Bay Hawks.
Southland is expecting to be bolstered by the arrival of Mike Helms.
Helms was a standout player for the now defunct Singapore Slingers in the Australian Basketball League, averaging more than 20 points.
