But Kellock is adamant fears of a mass exodus from Scotland are unfounded and told the 22-year-old to knuckle down for the remainder of the season at Firhill.
The Warriors face English Premiership side Bath in their Heineken Cup opener on Sunday and Kellock knows Richie and co will have to be at their best against the 1998 winners.
"Richie knows he has got a big season ahead of him and he wants to leave on a high," said Kellock.
"I am disappointed he is going on a personal note and for Glasgow. These things happen - it is professional sport and he was always going to get offers.
"We know it is going to be a step up but we are really excited to be playing a team that we do not play very often. There's a definite air of excitement.
"It will take our best performance. We will have to be at our best to compete against these big English Premiership teams.
"It is about us as well and in those Gloucester and Wasps games we went out there and played our best rugby. We did not sit back to see what they had to offer - we stamped our game on them and we have to do that again."
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