Quick question: my league is currently in the offseason.  I just traded for a player who is in his 3rd year of arbitration.  I accepted the trade yesterday, but arbitration ends today, and he won't be placed on my team until tomorrow I believe.  Will I be able to lock him up to a long term contract after he is placed on my team, or will he just be on his arbitration awarded contract and I could lose him to FA next season?  Thanks.

I think your best bet is to find out what he wants long term and have the current owner make an offer for you.

However, if the owner does sign him to a long term deal now the trade will be voided (change of contract).  So if you want to keep this guy your best bet is to have the owner offer the long term deal, then the trade gets voided then resubmit the trade offer

That's not true.

Typically, yes... if an owner offers an extension it will void the trade, but arbitration cases are different.

I've had the current owner offer both 1-year and multi-year deals to guys already part of an accepted trade, and it went through.