Alternatively, the Blues could look to add an offensive weapon via free agency.
With only eight forwards under contract for next season, and three pending restricted free agents, the Blues have space to fill up front and the salary cap space to do so.
The Blues have expressed an interest in Ottawa Senators captain Jason Spezza and are expected to revisit talks this off-season.
Spezza, 30, has one-year left on his contract. He's owed $4 million next season, but his cap hit is $7 million. He also owns a limited no-trade clause and can list up to 10 teams he will not accept a trade to.
Armstrong, should he go the free agency route, could target the likes of Minnesota Wild left wing Matt Moulson, Calgary Flames forward Mike Cammalleri, Colorado Avalanche center Paul Stastny and Senators forward Milan Michalek.