The goalkeeper joined the Championship outfit on an initial one-month deal and has opted to extend his stay at Riverside
The 37-year-old goalkeeper joined the Championship club on loan from Aston Villa on an initial one-month deal at the end of November and he has agreed to extend his time at Riverside after making seven appearances.
Middlesbrough chief executive, Neil Bausor, said that the club was "extremely delighted" that the Republic of Ireland international wanted to stay at the club.
"We are extremely delighted to secure the extension of Shay's loan until the end of February," he told the club's official website.
Meanwhile, Mick McCarthy has admitted his disappointment after a late goal denied Ipswich Town all three points against Charlton Athletic on New Year's Day.
The Tractor Boys had taken the lead in the first half through a Richard Wood own-goal, but Johnnie Jackson's 90th minute goal ensured a point for the Addicks.
"The fact we conceded late on leaves you feeling a bit deflated, annoyed and devastated," McCarthy told the BBC. "But it was a fair result.
"We could have killed it with the penalty but their goalkeeper's made a great save. It's another point and we're in the top six on New Year's Day. At the start of the season, I think we'd have taken that."