Underpair facing river bet 50nl

[Peleus]

Villain unknown.

Full Tilt Poker, $0.25/$0.50 NL Hold'em Cash Game, 6 Players
LeggoPoker Hand History Converter

BTN: $86.95
SB: $65.85
BB: $104.70
Hero (UTG): $117.05
MP: $19.95
CO: $52.75

Pre-Flop: 8[img]/images/graemlins/club.gif[/img] 8[img]/images/graemlins/diamond.gif[/img] dealt to Hero (UTG)
<font color="red">Hero raises to $1.75</font>, MP calls $1.75, 3 folds, BB calls $1.25

Flop: ($5.50) 5[img]/images/graemlins/heart.gif[/img] 2[img]/images/graemlins/diamond.gif[/img] J[img]/images/graemlins/heart.gif[/img] (3 Players)
BB checks, <font color="red">Hero bets $3</font>, MP calls $3, BB folds

Turn: ($11.50) 6[img]/images/graemlins/diamond.gif[/img] (2 Players)
Hero checks, MP checks

River: ($11.50) 3[img]/images/graemlins/club.gif[/img] (2 Players)
Hero checks, <font color="red">MP bets $5</font>, Hero ???

Whats your play against an unknown here.

[iRunBad123]

this is tough because there is a lot of 2 pair and straight combos but he could have a busted flush draw

[Profish2285]

I fold here against an unknown, looks more like a value bet than a bluff. I have been in this spot numerous times and everytime that I end up calling I look at a better hand.