The Saints are willing to let the 20-year-old leave on loan this summer to get regular game time.
However, Russell Martin admits that they need to ensure they have enough backup for the first team before finalizing any deal, amid interest from Celtic.
Martin told the Daily Echo: "With the squad as it is right now, not a chance. We need some reinforcements, I think.
"Ben Brereton Diaz is a good one but we need to make sure we get a few more in the building before the start (of the Premier League) if we can.
"Obviously, the transfer window stupidly, annoyingly and madly goes on until the end of August, which gives all the bigger clubs a massive advantage.
"It is what it is. So, yeah, we will bring some people in and assess the situation - but Shea was good tonight (against Oxford United)."