Mike Zimmer's poker face is as convincing as any football coach's, so he's never going to reveal a sense of alarm, even if his pulse is redlining like a Porsche.
If he's privately worried about the state of his offensive line as the Vikings enter Week 1, he refused to walk down that path with reporters on Monday.
That's understandable because coaches are experts at projecting calm and minimizing glaring trouble spots.
Count me among those with real concerns about Zimmer's offensive line.
The question mark hanging over that position group continued to grow and intensify as center John Sullivan missed another practice, apparently still recovering from back spasms, an injury that has sidelined the team's best lineman for three weeks.
Regardless of the public spin at Winter Park, Sullivan's prolonged absence represents another disconcerting development for a unit that has so much to prove this season.
Even if Sullivan returns to practice this week and plays in Monday's opener at San Francisco — which still is unknown at this point — the sensitive nature of a back injury creates worry that it could flare up on the 30-year-old again.
The offensive line already is taking on water and the season hasn't even started.