Feb 14 (Reuters) - Canada's main stock index fell on Monday, weighed down by energy stocks as crude prices fell after Ukraine hinted at possible concessions to Russia that could ease tensions between the two countries.

At 9:43 a.m. ET (14:43 GMT), the Toronto Stock Exchange's S&P/TSX composite index was down 143.28 points, or 0.66%, at 21,405.56 and was on track for its worst session in over a week.

"We're definitely setting up for a volatile week. Markets are swinging back and forth depending on Russian headlines, taking people into more defensive position," said Gregory Taylor, portfolio manager at Purpose Investments.

The energy sector dropped 1.0% as U.S. crude prices fell 0.7% a barrel, while Brent crude lost 0.8%.

Ukrainian Ambassador Vadym Prystaiko said his country was prepared to make some concessions to Russia, easing investor concerns that have rattled global equities following U.S. comments that Russia could invade Ukraine at any time.

"In energy we could see some profit taking because it has been the best performing sector the other day, but it won't go down too much," Taylor said.

Healthcare stocks fell 1% with major pot producers including Canopy Growth Corp, Cronos Group Inc, Aurora Cannabis Inc down between 1.5% and 3.1%.

Investors await earnings' reports from major companies this week including Shopify, Restaurant Brands, Canadian Tire, Air Canada and several big miners.

The materials sector, which includes precious and base metals miners and fertilizer companies, added 0.1% as gold futures rose 1.4% to $1,866 an ounce.

HIGHLIGHTS

The TSX posted two new 52-week highs and two new lows.

Across Canadian issues, there were nine new 52-week highs and 32 new lows, with total volume of 50.63 million shares.

(Reporting by Amal S in Bengaluru; Editing by Vinay Dwivedi)