Mike Vrabel put on a happy face for the newest member of the New England Patriots ... telling the team's first-round draft pick he's "doing great" on Thursday -- even though he's in the middle of a massive scandal with Dianna Russini.

The Pats shared footage from inside their draft room as they called offensive tackle Caleb Lomu to relay the life-changing news ... and the former Utah Ute was over the moon.

When the org's Executive Vice President of Player Personnel Eliot Wolf passed the phone to coach, he introduced himself and asked how Lomu was doing.

"I'm doing good, coach. How are you doing?" he replied.

It was an innocent response ... but given the recent news, it's pretty funny.

Vrabel didn't pour his heart out in the moment ... he said he's doing peachy as well.

Vrabel's actually skipping out on Day 3 of the draft to get counseling ... saying he's working on being the best version of himself after the recent dump of pics showing him having a lovely time with the NFL insider on several occasions over the years.

Vrabel also spoke prior to the event ... admitting his "previous actions don't meet the standards that I hold myself to."

Vrabel claimed he took accountability for his actions and acknowledged the massive distraction they caused.

Vrabel said he will work as long as it takes to be the person he expects of himself ... and thanked the team for the support he's gotten.