Dave Jones revealed today that he's kept an eye on the Arsenal player.
"We'd monitored him since the start of the season after the window closed," Jones told the club's official website.
"They were always looking to send him out to a Premier League club, but they didn't get that offer. Arsene (Wenger) decided that he wanted him to come here and we were pleased with that as we worked hard to get him.
"We had to hang in there as there were quite a few clubs chasing him."
Thomas will be in contention for the Watford game this Saturday.