Seamus Greene won the 2005 Senior Manx Grand Prix

Irish rider Seamus Greene, who has head injuries, is now in Walton Neurological Centre on Merseyside but is stable.

The condition of Jun Maeda from Japan has worsened and he is also now critical with pelvic injuries.

US sidecar passenger James Cornell remains critical with multiple injuries after crashing at May Hill on Saturday.

His driver Doug Dano, also from the USA, is comfortable in hospital.

Donegal man Greene and Maeda were airlifted to hospital after the accident on the Ballahutchin Straight.

The riders were in collision coming out of the Union Mills section about four miles onto the circuit.

The practice session was halted after the accident although it resumed later in the evening.

A TT spokesman said: "There was a two-bike incident coming out of Union Mills on the way to Glen Vine section.

"The riders involved were Jun Maeda and Seamus Greene, who were in collision, and both have been taken to hospital by helicopter."

Deaths are a regular occurrence at the Isle of Man TT

Monday's serious accident follows two other serious crashes in the Isle of Man over the weekend.

Sidecar racer Tony Smith and his passenger Barry Pepperrell were killed in a practice race for the Pre-TT Classic Road Races on Friday night.

This was followed on Saturday evening by the serious accident involving sidecar crew Dano and Cornell.

Martin Finnegan, on the Klaffi Honda Fireblade, was fastest in Monday's shortened practice session after registering a best lap time of 18 minutes and 38.32 seconds at an average speed of 121.457mph.

Guy Martin was second fastest, 4.17secs adrift, and Ian Lougher was third fastest though none could match the 18:33.23 benchmark set by John McGuinness on Saturday.

Martin was fastest in the Supersport class, but nevertheless slower than Ian Hutchison's Saturday standard, while Adrian Archibald led Monday's Superstock practice times though Bruce Anstey was faster on Saturday.