The defender rates the Slovak as one of the best goalkeepers he has played with, with Kello making vital saves in recent matches against Dundee United and Hearts.
Danny Lennon, the St Mirren manager, had been trying for some time to get Kello to extend his stay and McGregor believes it is a great bit of business to finally get it done. "I'm delighted that Marian is now staying until the end of the season," he said. "I know the gaffer and the chairman had been doing their utmost to keep him because he is probably the best goalkeeper I have played in front of.
"It breeds confidence when you know you have someone like him behind you. He's an unbelievable shot-stopper and I think he has saved three or four point-blank shots that would have been goals 90% of the time. It's great to have him and brilliant the gaffer has tied him up until the end of the season.
"When guys come in, the first couple of weeks they are quiet. But Marian has come out his shell a wee bit and he seems like a nice guy, a bit crazy, but I think all goalkeepers are."
St Mirren started this season with David Cornell between the posts but, with the Swansea City player having now returned to his parent club after an unsuccessful loan spell, the battle for the No.1 jersey will be between Kello and Christopher Dilo for the remainder of the season. McGregor believes French under-19 cap Dilo is also one to watch.
"A lot of people forget that Chris is a great keeper as well," he added. "He's only very young but when he came in he held his own. It was just unfortunate that when Marian came in, he went straight in, because he's experienced. But I'm sure if we need Chris' services he'll be ready."
Kello will likely be in goals for the Paisley side this afternoon when they travel to Rugby Park looking to bolster their chances of a top-six place. Kris Boyd has been in fine form for Kilmarnock of late and McGregor is looking forward to the challenge of keeping the veteran striker quiet. "He's very strong and he's the all-time top goalscorer in the SPL," he said. "He's prolific in and around the box and I know what I need to do against him. He's strong, physical and, although he'll probably admit he's not the quickest himself, you give him half a yard in the box and he'll punish you. I like playing against the best players because it's a test to see how good you are."
Kilmarnock were found wanting in only two of their last five fixtures, with the Ayrshire side having beaten each of Hearts, Partick Thistle and Ross County to close out 2013 nestled comfortably in the table. A defeat by Hibernian on Sunday might have caused Kilmarnock to lost balance at the turn of the year, yet Allan Johnston is content that his players have shown enough resolve of late to recover in Paisley.
"The boys are doing extremely well," said the Kilmarnock manager, whose side are just two points behind St Mirren in the league. "We weren't far away against Hibs and I don't think we merited a 3-0 defeat. It's been encouraging, the young players that have come in and the experienced players as well have gelled well together. We've got to carry our recent form through to 2014."