Though admitting he is "obviously concerned", Nicholls does not think that the horse will be unable to defend his Champion Chase title. If he regains fitness, Master Minded will not run for another three months at the earliest.
Nicholls told the Racing Post: "Whatever the outcome of the scan, I will run out of time to have him ready for the Tingle Creek and our main aim will be to get him right again for the Champion Chase.
"It may be he will end up having just the one run beforehand, in the Game Spirit at Newbury."
Meanwhile, The Listener will miss the rest of the season with a leg injury.
The 10-year-old was a 15-length winner of the Grade 1 JNwine.com Champion Chase at Down Royal on his reappearance 17 days ago, his fourth success at the top level.
Trainer Nick Mitchell said: "It's a major blow. I wasn't happy with the horse last Friday and we monitored him closely over the weekend, and it quickly became apparent something was amiss.
"It was decided to have his off-fore leg scanned at the yard and unfortunately that showed there is a minor problem with his tendon. It is enough to make us stop with him this year."