Mousinho noted transparent communication between the club and the player regarding future possibilities.
"Terry is really happy here, Terry is fully committed, we've said let's just stay open and honest about what happens elsewhere.
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We have seen in the past that, if a player really wants to go, it's very difficult to keep him should the offer be there and the offer is right," he said.
He reiterated that board decisions are driven by sporting logic rather than financial hardship.
"At absolutely no point of my time at this football club have we received an offer and the board have said we must sell the player for financial reasons.
That won't happen with Terry," Mousinho said.
The club's management approach mirrors previous high-profile squad decisions handled by the executive team.
"It will be more about what Terry wants to do and then, at that point, we will make that decision based on what we think is financially sensible for the football club.
We won't be strong-armed into anything," he said.
Mousinho compared the situation to prior mid-season transfers managed by Portsmouth.
"It's very, very similar to what happened in January with Callum Lang.
We were satisfied as a football club that we got the right price for the player and the player wanted to go - so we made the decision collectively," he said.
The manager added that the club maintains a firm valuation on the Northern Irish international.
"I think Terry deserves the praise, he deserves the limelight - and it's just about having an honest conversation with him," Mousinho said.
Portsmouth remains unwilling to lower its asking price for prospective buyers.
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"Maybe for our valuation of the player there might be a limited number of clubs who want to spend that on a right-back - and we're not going to shift from what we think Terry is worth," Mousinho said.
