The winger, who is on a year's contract with the Scarlets and Wales' Sevens had scored two tries in the Premiership fixture before sustaining a fracture and dislocation to his neck at the game held at St Helen's.
He was taken immediately to Morriston Hospital and then later transferred to the Heath hospital in Cardiff where he has undergone two operations.
Scarlets Head of Medical Andy Walker said: "Mike's injury was serious; the surgery undertaken has been successful and thankfully there has been no loss of function as a result of the injury. He will undergo a further CT scan later to ascertain whether he will need one further operation; however to date he has progressed well, the injury has been stabilised and he is recovering.
"On behalf of Mike, his family and the Scarlets we would like to express our gratitude to all the staff and medical teams at both Morriston and Heath Hospitals for their excellent work as they continue to monitor him. He is expected to remain in hospital for another week.
Simon Easterby, Scarlets Head Coach said: "Everyone at the Scarlets and especially the coaches and all our players send Mike and his family their very best wishes. We have been in close contact with the hospital teams, Mike and his family throughout and we are all pleased to see him making good progress."
ADDITIONAL SCARLETS INJURIES:
Aled Davies, scrum-half - knee swelling past two weeks. Recovered back into training next week.
Deacon Manu, Prop - progressing well from fractured arm. Back into non-contact training on Monday. Return expected end of January.
Sion Bennett:, back row - progressing well from shoulder dislocation. Expected return late March.
Jonathan Davies, centre - progressing well - light running. Fit for return early March.
Chris Knight, wing - dislocation of A/C joint during 7's. Surgery undertaken. Fit end of March.
Steven Shingler, centre - dislocation of A/C (shoulder) joint. Due to undergo surgery at the end of this week after further assessment and consultation. Likely to return early April.
Sione Timani - second/back row. Knee injury; ligament tear; in rehab likely out for 2/3 weeks.
Josh Lewis, outside half. Hamstring strain recovering well. Back into full training next week.
Liam Williams, full back: Fractured finger undergone treatment. Expected to be out for three weeks.
Ken Owens, hooker: ankle sprain, MRI scan showed no further damage. In rehab expected back in 2/3 weeks.
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