Tomkins has opted to cross codes for Saracens in a £250,000 deal - with Wigan also agreeing a long-term partnership with the Aviva Premiership champions
However Wigan have moved quickly to tie Joel's 22-year-old brother Sam to a new five-year deal that includes a clause preventing him speaking to either rugby union or NRL clubs in the next three years.
And Lenagan believes that the tables will soon turn, with players set to be encouraged to the 13-a-side code.
"I think rugby union and rugby league can work together quite closely," he said. "They are different games.
"I don't have any fears about losing players to rugby union. I think there is as much risk if not more of people going to the NRL because of the imbalance of the dollar and the pound.
"I think you'll see a lot of rugby union players coming back to rugby league because I think ours is a better game to watch and to play.
"We have no worry that we can keep generating players of the calibre of Joel. We're not threatened by it."
With little time to sign a replacement centre in time for the 2012 season and a shock move for Gareth Thomas falling through, new head coach Shaun Wane may have to promote from within.
Lenagan added: "We've looked around rugby league and there aren't really opportunities to get a centre of the right calibre to come to Wigan at this stage.
"We could go to Australia and get a middle-grade £100,000-plus-a-year centre but we don't want to do that.
"We would rather give young English players an opportunity. Darrell Goulding, for example, will get his opportunity again and Josh Charnley is another potential centre."
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